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unistr.h (188891B)

---

// © 2016 and later: Unicode, Inc. and others.
// License & terms of use: http://www.unicode.org/copyright.html
/*
**********************************************************************
*   Copyright (C) 1998-2016, International Business Machines
*   Corporation and others.  All Rights Reserved.
**********************************************************************
*
* File unistr.h
*
* Modification History:
*
*   Date        Name        Description
*   09/25/98    stephen     Creation.
*   11/11/98    stephen     Changed per 11/9 code review.
*   04/20/99    stephen     Overhauled per 4/16 code review.
*   11/18/99    aliu        Made to inherit from Replaceable.  Added method
*                           handleReplaceBetween(); other methods unchanged.
*   06/25/01    grhoten     Remove dependency on iostream.
******************************************************************************
*/

#ifndef UNISTR_H
#define UNISTR_H

/**
* \file
* \brief C++ API: Unicode String
*/

#include "unicode/utypes.h"

#if U_SHOW_CPLUSPLUS_API

#include <cstddef>
#include <string_view>
#include "unicode/char16ptr.h"
#include "unicode/rep.h"
#include "unicode/std_string.h"
#include "unicode/stringpiece.h"
#include "unicode/bytestream.h"

struct UConverter;          // unicode/ucnv.h

#ifndef USTRING_H
/**
* \ingroup ustring_ustrlen
* @param s Pointer to sequence of UChars.
* @return Length of sequence.
*/
U_CAPI int32_t U_EXPORT2 u_strlen(const UChar *s);
#endif

U_NAMESPACE_BEGIN

#if !UCONFIG_NO_BREAK_ITERATION
class BreakIterator;        // unicode/brkiter.h
#endif
class Edits;

U_NAMESPACE_END

// Not #ifndef U_HIDE_INTERNAL_API because UnicodeString needs the UStringCaseMapper.
/**
* Internal string case mapping function type.
* All error checking must be done.
* src and dest must not overlap.
* @internal
*/
typedef int32_t U_CALLCONV
UStringCaseMapper(int32_t caseLocale, uint32_t options,
#if !UCONFIG_NO_BREAK_ITERATION
                 icu::BreakIterator *iter,
#endif
                 char16_t *dest, int32_t destCapacity,
                 const char16_t *src, int32_t srcLength,
                 icu::Edits *edits,
                 UErrorCode &errorCode);

U_NAMESPACE_BEGIN

class Locale;               // unicode/locid.h
class StringCharacterIterator;
class UnicodeStringAppendable;  // unicode/appendable.h

/* The <iostream> include has been moved to unicode/ustream.h */

/**
* Constant to be used in the UnicodeString(char *, int32_t, EInvariant) constructor
* which constructs a Unicode string from an invariant-character char * string.
* About invariant characters see utypes.h.
* This constructor has no runtime dependency on conversion code and is
* therefore recommended over ones taking a charset name string
* (where the empty string "" indicates invariant-character conversion).
*
* @stable ICU 3.2
*/
#define US_INV icu::UnicodeString::kInvariant

/**
* \def UNICODE_STRING
* Obsolete macro approximating UnicodeString literals.
*
* Prior to the availability of C++11 and u"UTF-16 string literals",
* this macro was provided for portability and efficiency when
* initializing UnicodeStrings from literals.
*
* Since C++17 and ICU 76, you can use UTF-16 string literals with compile-time
* length determination:
* \code
* UnicodeString str(u"literal");
* if (str == u"other literal") { ... }
* \endcode
*
* The string parameter must be a C string literal.
* The length of the string, not including the terminating
* `NUL`, must be specified as a constant.
* @stable ICU 2.0
*/
#if !U_CHAR16_IS_TYPEDEF
# define UNICODE_STRING(cs, _length) icu::UnicodeString(true, u ## cs, _length)
#else
# define UNICODE_STRING(cs, _length) icu::UnicodeString(true, (const char16_t*)u ## cs, _length)
#endif

/**
* Unicode String literals in C++.
* Obsolete macro approximating UnicodeString literals.
* See UNICODE_STRING.
*
* The string parameter must be a C string literal.
* @stable ICU 2.0
* @see UNICODE_STRING
*/
#define UNICODE_STRING_SIMPLE(cs) UNICODE_STRING(cs, -1)

/**
* \def UNISTR_FROM_CHAR_EXPLICIT
* This can be defined to be empty or "explicit".
* If explicit, then the UnicodeString(char16_t) and UnicodeString(UChar32)
* constructors are marked as explicit, preventing their inadvertent use.
* @stable ICU 49
*/
#ifndef UNISTR_FROM_CHAR_EXPLICIT
# if defined(U_COMBINED_IMPLEMENTATION) || defined(U_COMMON_IMPLEMENTATION) || defined(U_I18N_IMPLEMENTATION) || defined(U_IO_IMPLEMENTATION)
   // Auto-"explicit" in ICU library code.
#   define UNISTR_FROM_CHAR_EXPLICIT explicit
# else
   // Empty by default for source code compatibility.
#   define UNISTR_FROM_CHAR_EXPLICIT
# endif
#endif

/**
* \def UNISTR_FROM_STRING_EXPLICIT
* This can be defined to be empty or "explicit".
* If explicit, then the UnicodeString(const char *) and UnicodeString(const char16_t *)
* constructors are marked as explicit, preventing their inadvertent use.
*
* In particular, this helps prevent accidentally depending on ICU conversion code
* by passing a string literal into an API with a const UnicodeString & parameter.
* @stable ICU 49
*/
#ifndef UNISTR_FROM_STRING_EXPLICIT
# if defined(U_COMBINED_IMPLEMENTATION) || defined(U_COMMON_IMPLEMENTATION) || defined(U_I18N_IMPLEMENTATION) || defined(U_IO_IMPLEMENTATION)
   // Auto-"explicit" in ICU library code.
#   define UNISTR_FROM_STRING_EXPLICIT explicit
# else
   // Empty by default for source code compatibility.
#   define UNISTR_FROM_STRING_EXPLICIT
# endif
#endif

/**
* \def UNISTR_OBJECT_SIZE
* Desired sizeof(UnicodeString) in bytes.
* It should be a multiple of sizeof(pointer) to avoid unusable space for padding.
* The object size may want to be a multiple of 16 bytes,
* which is a common granularity for heap allocation.
*
* Any space inside the object beyond sizeof(vtable pointer) + 2
* is available for storing short strings inside the object.
* The bigger the object, the longer a string that can be stored inside the object,
* without additional heap allocation.
*
* Depending on a platform's pointer size, pointer alignment requirements,
* and struct padding, the compiler will usually round up sizeof(UnicodeString)
* to 4 * sizeof(pointer) (or 3 * sizeof(pointer) for P128 data models),
* to hold the fields for heap-allocated strings.
* Such a minimum size also ensures that the object is easily large enough
* to hold at least 2 char16_ts, for one supplementary code point (U16_MAX_LENGTH).
*
* sizeof(UnicodeString) >= 48 should work for all known platforms.
*
* For example, on a 64-bit machine where sizeof(vtable pointer) is 8,
* sizeof(UnicodeString) = 64 would leave space for
* (64 - sizeof(vtable pointer) - 2) / U_SIZEOF_UCHAR = (64 - 8 - 2) / 2 = 27
* char16_ts stored inside the object.
*
* The minimum object size on a 64-bit machine would be
* 4 * sizeof(pointer) = 4 * 8 = 32 bytes,
* and the internal buffer would hold up to 11 char16_ts in that case.
*
* @see U16_MAX_LENGTH
* @stable ICU 56
*/
#ifndef UNISTR_OBJECT_SIZE
# define UNISTR_OBJECT_SIZE 64
#endif

/**
* UnicodeString is a string class that stores Unicode characters directly and provides
* similar functionality as the Java String and StringBuffer/StringBuilder classes.
* It is a concrete implementation of the abstract class Replaceable (for transliteration).
*
* The UnicodeString equivalent of std::string’s clear() is remove().
*
* Starting with ICU 78, a UnicodeString is a C++ "range" of char16_t code units.
* utfStringCodePoints() and unsafeUTFStringCodePoints() can be used to iterate over
* the code points.
*
* A UnicodeString may "alias" an external array of characters
* (that is, point to it, rather than own the array)
* whose lifetime must then at least match the lifetime of the aliasing object.
* This aliasing may be preserved when returning a UnicodeString by value,
* depending on the compiler and the function implementation,
* via Return Value Optimization (RVO) or the move assignment operator.
* (However, the copy assignment operator does not preserve aliasing.)
* For details see the description of storage models at the end of the class API docs
* and in the User Guide chapter linked from there.
*
* The UnicodeString class is not suitable for subclassing.
*
* For an overview of Unicode strings in C and C++ see the
* [User Guide Strings chapter](https://unicode-org.github.io/icu/userguide/strings#strings-in-cc).
*
* In ICU, a Unicode string consists of 16-bit Unicode *code units*.
* A Unicode character may be stored with either one code unit
* (the most common case) or with a matched pair of special code units
* ("surrogates"). The data type for code units is char16_t.
* For single-character handling, a Unicode character code *point* is a value
* in the range 0..0x10ffff. ICU uses the UChar32 type for code points.
*
* Indexes and offsets into and lengths of strings always count code units, not code points.
* This is the same as with multi-byte char* strings in traditional string handling.
* Operations on partial strings typically do not test for code point boundaries.
* If necessary, the user needs to take care of such boundaries by testing for the code unit
* values or by using functions like
* UnicodeString::getChar32Start() and UnicodeString::getChar32Limit()
* (or, in C, the equivalent macros U16_SET_CP_START() and U16_SET_CP_LIMIT(), see utf.h).
*
* UnicodeString methods are more lenient with regard to input parameter values
* than other ICU APIs. In particular:
* - If indexes are out of bounds for a UnicodeString object
*   (< 0 or > length()) then they are "pinned" to the nearest boundary.
* - If the buffer passed to an insert/append/replace operation is owned by the
*   target object, e.g., calling str.append(str), an extra copy may take place
*   to ensure safety.
* - If primitive string pointer values (e.g., const char16_t * or char *)
*   for input strings are nullptr, then those input string parameters are treated
*   as if they pointed to an empty string.
*   However, this is *not* the case for char * parameters for charset names
*   or other IDs.
* - Most UnicodeString methods do not take a UErrorCode parameter because
*   there are usually very few opportunities for failure other than a shortage
*   of memory, error codes in low-level C++ string methods would be inconvenient,
*   and the error code as the last parameter (ICU convention) would prevent
*   the use of default parameter values.
*   Instead, such methods set the UnicodeString into a "bogus" state
*   (see isBogus()) if an error occurs.
*
* In string comparisons, two UnicodeString objects that are both "bogus"
* compare equal (to be transitive and prevent endless loops in sorting),
* and a "bogus" string compares less than any non-"bogus" one.
*
* Const UnicodeString methods are thread-safe. Multiple threads can use
* const methods on the same UnicodeString object simultaneously,
* but non-const methods must not be called concurrently (in multiple threads)
* with any other (const or non-const) methods.
*
* Similarly, const UnicodeString & parameters are thread-safe.
* One object may be passed in as such a parameter concurrently in multiple threads.
* This includes the const UnicodeString & parameters for
* copy construction, assignment, and cloning.
*
* UnicodeString uses several storage methods.
* String contents can be stored inside the UnicodeString object itself,
* in an allocated and shared buffer, or in an outside buffer that is "aliased".
* Most of this is done transparently, but careful aliasing in particular provides
* significant performance improvements.
* Also, the internal buffer is accessible via special functions.
* For details see the
* [User Guide Strings chapter](https://unicode-org.github.io/icu/userguide/strings#maximizing-performance-with-the-unicodestring-storage-model).
*
* @see utf.h
* @see utfiterator.h
* @see utfStringCodePoints
* @see unsafeUTFStringCodePoints
* @see CharacterIterator
* @stable ICU 2.0
*/
class U_COMMON_API UnicodeString : public Replaceable
{
public:
 /** C++ boilerplate @internal */
 using value_type = char16_t;

 /**
  * Constant to be used in the UnicodeString(char *, int32_t, EInvariant) constructor
  * which constructs a Unicode string from an invariant-character char * string.
  * Use the macro US_INV instead of the full qualification for this value.
  *
  * @see US_INV
  * @stable ICU 3.2
  */
 enum EInvariant {
   /**
    * @see EInvariant
    * @stable ICU 3.2
    */
   kInvariant
 };

 //========================================
 // Read-only operations
 //========================================

 /* Comparison - bitwise only - for international comparison use collation */

 /**
  * Equality operator. Performs only bitwise comparison.
  * @param text The UnicodeString to compare to this one.
  * @return true if `text` contains the same characters as this one,
  * false otherwise.
  * @stable ICU 2.0
  */
 inline bool operator== (const UnicodeString& text) const;

 /**
  * Equality operator. Performs only bitwise comparison with `text`
  * which is, or which is implicitly convertible to,
  * a std::u16string_view or (if U_SIZEOF_WCHAR_T==2) std::wstring_view.
  *
  * For performance, you can use UTF-16 string literals with compile-time
  * length determination:
  * \code
  * UnicodeString str = ...;
  * if (str == u"literal") { ... }
  * \endcode
  * @param text The string view to compare to this string.
  * @return true if `text` contains the same characters as this one, false otherwise.
  * @stable ICU 76
  */
 template<typename S, typename = std::enable_if_t<ConvertibleToU16StringView<S>>>
 inline bool operator==(const S &text) const {
   std::u16string_view sv(internal::toU16StringView(text));
   uint32_t len;  // unsigned to avoid a compiler warning
   return !isBogus() && (len = length()) == sv.length() && doEquals(sv.data(), len);
 }

 /**
  * Inequality operator. Performs only bitwise comparison.
  * @param text The UnicodeString to compare to this one.
  * @return false if `text` contains the same characters as this one,
  * true otherwise.
  * @stable ICU 2.0
  */
 inline bool operator!= (const UnicodeString& text) const;

 /**
  * Inequality operator. Performs only bitwise comparison with `text`
  * which is, or which is implicitly convertible to,
  * a std::u16string_view or (if U_SIZEOF_WCHAR_T==2) std::wstring_view.
  *
  * For performance, you can use std::u16string_view literals with compile-time
  * length determination:
  * \code
  * #include &lt;string_view&gt;
  * using namespace std::string_view_literals;
  * UnicodeString str = ...;
  * if (str != u"literal"sv) { ... }
  * \endcode
  * @param text The string view to compare to this string.
  * @return false if `text` contains the same characters as this one, true otherwise.
  * @stable ICU 76
  */
 template<typename S, typename = std::enable_if_t<ConvertibleToU16StringView<S>>>
 inline bool operator!=(const S &text) const {
   return !operator==(text);
 }

 /**
  * Greater than operator. Performs only bitwise comparison.
  * @param text The UnicodeString to compare to this one.
  * @return true if the characters in this are bitwise
  * greater than the characters in `text`, false otherwise
  * @stable ICU 2.0
  */
 inline UBool operator> (const UnicodeString& text) const;

 /**
  * Less than operator. Performs only bitwise comparison.
  * @param text The UnicodeString to compare to this one.
  * @return true if the characters in this are bitwise
  * less than the characters in `text`, false otherwise
  * @stable ICU 2.0
  */
 inline UBool operator< (const UnicodeString& text) const;

 /**
  * Greater than or equal operator. Performs only bitwise comparison.
  * @param text The UnicodeString to compare to this one.
  * @return true if the characters in this are bitwise
  * greater than or equal to the characters in `text`, false otherwise
  * @stable ICU 2.0
  */
 inline UBool operator>= (const UnicodeString& text) const;

 /**
  * Less than or equal operator. Performs only bitwise comparison.
  * @param text The UnicodeString to compare to this one.
  * @return true if the characters in this are bitwise
  * less than or equal to the characters in `text`, false otherwise
  * @stable ICU 2.0
  */
 inline UBool operator<= (const UnicodeString& text) const;

 /**
  * Compare the characters bitwise in this UnicodeString to
  * the characters in `text`.
  * @param text The UnicodeString to compare to this one.
  * @return The result of bitwise character comparison: 0 if this
  * contains the same characters as `text`, -1 if the characters in
  * this are bitwise less than the characters in `text`, +1 if the
  * characters in this are bitwise greater than the characters
  * in `text`.
  * @stable ICU 2.0
  */
 inline int8_t compare(const UnicodeString& text) const;

 /**
  * Compare the characters bitwise in the range
  * [`start`, `start + length`) with the characters
  * in the **entire string** `text`.
  * (The parameters "start" and "length" are not applied to the other text "text".)
  * @param start the offset at which the compare operation begins
  * @param length the number of characters of text to compare.
  * @param text the other text to be compared against this string.
  * @return The result of bitwise character comparison: 0 if this
  * contains the same characters as `text`, -1 if the characters in
  * this are bitwise less than the characters in `text`, +1 if the
  * characters in this are bitwise greater than the characters
  * in `text`.
  * @stable ICU 2.0
  */
 inline int8_t compare(int32_t start,
        int32_t length,
        const UnicodeString& text) const;

 /**
  * Compare the characters bitwise in the range
  * [`start`, `start + length`) with the characters
  * in `srcText` in the range
  * [`srcStart`, `srcStart + srcLength`).
  * @param start the offset at which the compare operation begins
  * @param length the number of characters in this to compare.
  * @param srcText the text to be compared
  * @param srcStart the offset into `srcText` to start comparison
  * @param srcLength the number of characters in `src` to compare
  * @return The result of bitwise character comparison: 0 if this
  * contains the same characters as `srcText`, -1 if the characters in
  * this are bitwise less than the characters in `srcText`, +1 if the
  * characters in this are bitwise greater than the characters
  * in `srcText`.
  * @stable ICU 2.0
  */
  inline int8_t compare(int32_t start,
        int32_t length,
        const UnicodeString& srcText,
        int32_t srcStart,
        int32_t srcLength) const;

 /**
  * Compare the characters bitwise in this UnicodeString with the first
  * `srcLength` characters in `srcChars`.
  * @param srcChars The characters to compare to this UnicodeString.
  * @param srcLength the number of characters in `srcChars` to compare
  * @return The result of bitwise character comparison: 0 if this
  * contains the same characters as `srcChars`, -1 if the characters in
  * this are bitwise less than the characters in `srcChars`, +1 if the
  * characters in this are bitwise greater than the characters
  * in `srcChars`.
  * @stable ICU 2.0
  */
 inline int8_t compare(ConstChar16Ptr srcChars,
        int32_t srcLength) const;

 /**
  * Compare the characters bitwise in the range
  * [`start`, `start + length`) with the first
  * `length` characters in `srcChars`
  * @param start the offset at which the compare operation begins
  * @param length the number of characters to compare.
  * @param srcChars the characters to be compared
  * @return The result of bitwise character comparison: 0 if this
  * contains the same characters as `srcChars`, -1 if the characters in
  * this are bitwise less than the characters in `srcChars`, +1 if the
  * characters in this are bitwise greater than the characters
  * in `srcChars`.
  * @stable ICU 2.0
  */
 inline int8_t compare(int32_t start,
        int32_t length,
        const char16_t *srcChars) const;

 /**
  * Compare the characters bitwise in the range
  * [`start`, `start + length`) with the characters
  * in `srcChars` in the range
  * [`srcStart`, `srcStart + srcLength`).
  * @param start the offset at which the compare operation begins
  * @param length the number of characters in this to compare
  * @param srcChars the characters to be compared
  * @param srcStart the offset into `srcChars` to start comparison
  * @param srcLength the number of characters in `srcChars` to compare
  * @return The result of bitwise character comparison: 0 if this
  * contains the same characters as `srcChars`, -1 if the characters in
  * this are bitwise less than the characters in `srcChars`, +1 if the
  * characters in this are bitwise greater than the characters
  * in `srcChars`.
  * @stable ICU 2.0
  */
 inline int8_t compare(int32_t start,
        int32_t length,
        const char16_t *srcChars,
        int32_t srcStart,
        int32_t srcLength) const;

 /**
  * Compare the characters bitwise in the range
  * [`start`, `limit`) with the characters
  * in `srcText` in the range
  * [`srcStart`, `srcLimit`).
  * @param start the offset at which the compare operation begins
  * @param limit the offset immediately following the compare operation
  * @param srcText the text to be compared
  * @param srcStart the offset into `srcText` to start comparison
  * @param srcLimit the offset into `srcText` to limit comparison
  * @return The result of bitwise character comparison: 0 if this
  * contains the same characters as `srcText`, -1 if the characters in
  * this are bitwise less than the characters in `srcText`, +1 if the
  * characters in this are bitwise greater than the characters
  * in `srcText`.
  * @stable ICU 2.0
  */
 inline int8_t compareBetween(int32_t start,
           int32_t limit,
           const UnicodeString& srcText,
           int32_t srcStart,
           int32_t srcLimit) const;

 /**
  * Compare two Unicode strings in code point order.
  * The result may be different from the results of compare(), operator<, etc.
  * if supplementary characters are present:
  *
  * In UTF-16, supplementary characters (with code points U+10000 and above) are
  * stored with pairs of surrogate code units. These have values from 0xd800 to 0xdfff,
  * which means that they compare as less than some other BMP characters like U+feff.
  * This function compares Unicode strings in code point order.
  * If either of the UTF-16 strings is malformed (i.e., it contains unpaired surrogates), then the result is not defined.
  *
  * @param text Another string to compare this one to.
  * @return a negative/zero/positive integer corresponding to whether
  * this string is less than/equal to/greater than the second one
  * in code point order
  * @stable ICU 2.0
  */
 inline int8_t compareCodePointOrder(const UnicodeString& text) const;

 /**
  * Compare two Unicode strings in code point order.
  * The result may be different from the results of compare(), operator<, etc.
  * if supplementary characters are present:
  *
  * In UTF-16, supplementary characters (with code points U+10000 and above) are
  * stored with pairs of surrogate code units. These have values from 0xd800 to 0xdfff,
  * which means that they compare as less than some other BMP characters like U+feff.
  * This function compares Unicode strings in code point order.
  * If either of the UTF-16 strings is malformed (i.e., it contains unpaired surrogates), then the result is not defined.
  *
  * @param start The start offset in this string at which the compare operation begins.
  * @param length The number of code units from this string to compare.
  * @param srcText Another string to compare this one to.
  * @return a negative/zero/positive integer corresponding to whether
  * this string is less than/equal to/greater than the second one
  * in code point order
  * @stable ICU 2.0
  */
 inline int8_t compareCodePointOrder(int32_t start,
                                     int32_t length,
                                     const UnicodeString& srcText) const;

 /**
  * Compare two Unicode strings in code point order.
  * The result may be different from the results of compare(), operator<, etc.
  * if supplementary characters are present:
  *
  * In UTF-16, supplementary characters (with code points U+10000 and above) are
  * stored with pairs of surrogate code units. These have values from 0xd800 to 0xdfff,
  * which means that they compare as less than some other BMP characters like U+feff.
  * This function compares Unicode strings in code point order.
  * If either of the UTF-16 strings is malformed (i.e., it contains unpaired surrogates), then the result is not defined.
  *
  * @param start The start offset in this string at which the compare operation begins.
  * @param length The number of code units from this string to compare.
  * @param srcText Another string to compare this one to.
  * @param srcStart The start offset in that string at which the compare operation begins.
  * @param srcLength The number of code units from that string to compare.
  * @return a negative/zero/positive integer corresponding to whether
  * this string is less than/equal to/greater than the second one
  * in code point order
  * @stable ICU 2.0
  */
  inline int8_t compareCodePointOrder(int32_t start,
                                      int32_t length,
                                      const UnicodeString& srcText,
                                      int32_t srcStart,
                                      int32_t srcLength) const;

 /**
  * Compare two Unicode strings in code point order.
  * The result may be different from the results of compare(), operator<, etc.
  * if supplementary characters are present:
  *
  * In UTF-16, supplementary characters (with code points U+10000 and above) are
  * stored with pairs of surrogate code units. These have values from 0xd800 to 0xdfff,
  * which means that they compare as less than some other BMP characters like U+feff.
  * This function compares Unicode strings in code point order.
  * If either of the UTF-16 strings is malformed (i.e., it contains unpaired surrogates), then the result is not defined.
  *
  * @param srcChars A pointer to another string to compare this one to.
  * @param srcLength The number of code units from that string to compare.
  * @return a negative/zero/positive integer corresponding to whether
  * this string is less than/equal to/greater than the second one
  * in code point order
  * @stable ICU 2.0
  */
 inline int8_t compareCodePointOrder(ConstChar16Ptr srcChars,
                                     int32_t srcLength) const;

 /**
  * Compare two Unicode strings in code point order.
  * The result may be different from the results of compare(), operator<, etc.
  * if supplementary characters are present:
  *
  * In UTF-16, supplementary characters (with code points U+10000 and above) are
  * stored with pairs of surrogate code units. These have values from 0xd800 to 0xdfff,
  * which means that they compare as less than some other BMP characters like U+feff.
  * This function compares Unicode strings in code point order.
  * If either of the UTF-16 strings is malformed (i.e., it contains unpaired surrogates), then the result is not defined.
  *
  * @param start The start offset in this string at which the compare operation begins.
  * @param length The number of code units from this string to compare.
  * @param srcChars A pointer to another string to compare this one to.
  * @return a negative/zero/positive integer corresponding to whether
  * this string is less than/equal to/greater than the second one
  * in code point order
  * @stable ICU 2.0
  */
 inline int8_t compareCodePointOrder(int32_t start,
                                     int32_t length,
                                     const char16_t *srcChars) const;

 /**
  * Compare two Unicode strings in code point order.
  * The result may be different from the results of compare(), operator<, etc.
  * if supplementary characters are present:
  *
  * In UTF-16, supplementary characters (with code points U+10000 and above) are
  * stored with pairs of surrogate code units. These have values from 0xd800 to 0xdfff,
  * which means that they compare as less than some other BMP characters like U+feff.
  * This function compares Unicode strings in code point order.
  * If either of the UTF-16 strings is malformed (i.e., it contains unpaired surrogates), then the result is not defined.
  *
  * @param start The start offset in this string at which the compare operation begins.
  * @param length The number of code units from this string to compare.
  * @param srcChars A pointer to another string to compare this one to.
  * @param srcStart The start offset in that string at which the compare operation begins.
  * @param srcLength The number of code units from that string to compare.
  * @return a negative/zero/positive integer corresponding to whether
  * this string is less than/equal to/greater than the second one
  * in code point order
  * @stable ICU 2.0
  */
 inline int8_t compareCodePointOrder(int32_t start,
                                     int32_t length,
                                     const char16_t *srcChars,
                                     int32_t srcStart,
                                     int32_t srcLength) const;

 /**
  * Compare two Unicode strings in code point order.
  * The result may be different from the results of compare(), operator<, etc.
  * if supplementary characters are present:
  *
  * In UTF-16, supplementary characters (with code points U+10000 and above) are
  * stored with pairs of surrogate code units. These have values from 0xd800 to 0xdfff,
  * which means that they compare as less than some other BMP characters like U+feff.
  * This function compares Unicode strings in code point order.
  * If either of the UTF-16 strings is malformed (i.e., it contains unpaired surrogates), then the result is not defined.
  *
  * @param start The start offset in this string at which the compare operation begins.
  * @param limit The offset after the last code unit from this string to compare.
  * @param srcText Another string to compare this one to.
  * @param srcStart The start offset in that string at which the compare operation begins.
  * @param srcLimit The offset after the last code unit from that string to compare.
  * @return a negative/zero/positive integer corresponding to whether
  * this string is less than/equal to/greater than the second one
  * in code point order
  * @stable ICU 2.0
  */
 inline int8_t compareCodePointOrderBetween(int32_t start,
                                            int32_t limit,
                                            const UnicodeString& srcText,
                                            int32_t srcStart,
                                            int32_t srcLimit) const;

 /**
  * Compare two strings case-insensitively using full case folding.
  * This is equivalent to this->foldCase(options).compare(text.foldCase(options)).
  *
  * @param text Another string to compare this one to.
  * @param options A bit set of options:
  *   - U_FOLD_CASE_DEFAULT or 0 is used for default options:
  *     Comparison in code unit order with default case folding.
  *
  *   - U_COMPARE_CODE_POINT_ORDER
  *     Set to choose code point order instead of code unit order
  *     (see u_strCompare for details).
  *
  *   - U_FOLD_CASE_EXCLUDE_SPECIAL_I
  *
  * @return A negative, zero, or positive integer indicating the comparison result.
  * @stable ICU 2.0
  */
 inline int8_t caseCompare(const UnicodeString& text, uint32_t options) const;

 /**
  * Compare two strings case-insensitively using full case folding.
  * This is equivalent to this->foldCase(options).compare(srcText.foldCase(options)).
  *
  * @param start The start offset in this string at which the compare operation begins.
  * @param length The number of code units from this string to compare.
  * @param srcText Another string to compare this one to.
  * @param options A bit set of options:
  *   - U_FOLD_CASE_DEFAULT or 0 is used for default options:
  *     Comparison in code unit order with default case folding.
  *
  *   - U_COMPARE_CODE_POINT_ORDER
  *     Set to choose code point order instead of code unit order
  *     (see u_strCompare for details).
  *
  *   - U_FOLD_CASE_EXCLUDE_SPECIAL_I
  *
  * @return A negative, zero, or positive integer indicating the comparison result.
  * @stable ICU 2.0
  */
 inline int8_t caseCompare(int32_t start,
        int32_t length,
        const UnicodeString& srcText,
        uint32_t options) const;

 /**
  * Compare two strings case-insensitively using full case folding.
  * This is equivalent to this->foldCase(options).compare(srcText.foldCase(options)).
  *
  * @param start The start offset in this string at which the compare operation begins.
  * @param length The number of code units from this string to compare.
  * @param srcText Another string to compare this one to.
  * @param srcStart The start offset in that string at which the compare operation begins.
  * @param srcLength The number of code units from that string to compare.
  * @param options A bit set of options:
  *   - U_FOLD_CASE_DEFAULT or 0 is used for default options:
  *     Comparison in code unit order with default case folding.
  *
  *   - U_COMPARE_CODE_POINT_ORDER
  *     Set to choose code point order instead of code unit order
  *     (see u_strCompare for details).
  *
  *   - U_FOLD_CASE_EXCLUDE_SPECIAL_I
  *
  * @return A negative, zero, or positive integer indicating the comparison result.
  * @stable ICU 2.0
  */
 inline int8_t caseCompare(int32_t start,
        int32_t length,
        const UnicodeString& srcText,
        int32_t srcStart,
        int32_t srcLength,
        uint32_t options) const;

 /**
  * Compare two strings case-insensitively using full case folding.
  * This is equivalent to this->foldCase(options).compare(srcChars.foldCase(options)).
  *
  * @param srcChars A pointer to another string to compare this one to.
  * @param srcLength The number of code units from that string to compare.
  * @param options A bit set of options:
  *   - U_FOLD_CASE_DEFAULT or 0 is used for default options:
  *     Comparison in code unit order with default case folding.
  *
  *   - U_COMPARE_CODE_POINT_ORDER
  *     Set to choose code point order instead of code unit order
  *     (see u_strCompare for details).
  *
  *   - U_FOLD_CASE_EXCLUDE_SPECIAL_I
  *
  * @return A negative, zero, or positive integer indicating the comparison result.
  * @stable ICU 2.0
  */
 inline int8_t caseCompare(ConstChar16Ptr srcChars,
        int32_t srcLength,
        uint32_t options) const;

 /**
  * Compare two strings case-insensitively using full case folding.
  * This is equivalent to this->foldCase(options).compare(srcChars.foldCase(options)).
  *
  * @param start The start offset in this string at which the compare operation begins.
  * @param length The number of code units from this string to compare.
  * @param srcChars A pointer to another string to compare this one to.
  * @param options A bit set of options:
  *   - U_FOLD_CASE_DEFAULT or 0 is used for default options:
  *     Comparison in code unit order with default case folding.
  *
  *   - U_COMPARE_CODE_POINT_ORDER
  *     Set to choose code point order instead of code unit order
  *     (see u_strCompare for details).
  *
  *   - U_FOLD_CASE_EXCLUDE_SPECIAL_I
  *
  * @return A negative, zero, or positive integer indicating the comparison result.
  * @stable ICU 2.0
  */
 inline int8_t caseCompare(int32_t start,
        int32_t length,
        const char16_t *srcChars,
        uint32_t options) const;

 /**
  * Compare two strings case-insensitively using full case folding.
  * This is equivalent to this->foldCase(options).compare(srcChars.foldCase(options)).
  *
  * @param start The start offset in this string at which the compare operation begins.
  * @param length The number of code units from this string to compare.
  * @param srcChars A pointer to another string to compare this one to.
  * @param srcStart The start offset in that string at which the compare operation begins.
  * @param srcLength The number of code units from that string to compare.
  * @param options A bit set of options:
  *   - U_FOLD_CASE_DEFAULT or 0 is used for default options:
  *     Comparison in code unit order with default case folding.
  *
  *   - U_COMPARE_CODE_POINT_ORDER
  *     Set to choose code point order instead of code unit order
  *     (see u_strCompare for details).
  *
  *   - U_FOLD_CASE_EXCLUDE_SPECIAL_I
  *
  * @return A negative, zero, or positive integer indicating the comparison result.
  * @stable ICU 2.0
  */
 inline int8_t caseCompare(int32_t start,
        int32_t length,
        const char16_t *srcChars,
        int32_t srcStart,
        int32_t srcLength,
        uint32_t options) const;

 /**
  * Compare two strings case-insensitively using full case folding.
  * This is equivalent to this->foldCase(options).compareBetween(text.foldCase(options)).
  *
  * @param start The start offset in this string at which the compare operation begins.
  * @param limit The offset after the last code unit from this string to compare.
  * @param srcText Another string to compare this one to.
  * @param srcStart The start offset in that string at which the compare operation begins.
  * @param srcLimit The offset after the last code unit from that string to compare.
  * @param options A bit set of options:
  *   - U_FOLD_CASE_DEFAULT or 0 is used for default options:
  *     Comparison in code unit order with default case folding.
  *
  *   - U_COMPARE_CODE_POINT_ORDER
  *     Set to choose code point order instead of code unit order
  *     (see u_strCompare for details).
  *
  *   - U_FOLD_CASE_EXCLUDE_SPECIAL_I
  *
  * @return A negative, zero, or positive integer indicating the comparison result.
  * @stable ICU 2.0
  */
 inline int8_t caseCompareBetween(int32_t start,
           int32_t limit,
           const UnicodeString& srcText,
           int32_t srcStart,
           int32_t srcLimit,
           uint32_t options) const;

 /**
  * Determine if this starts with the characters in `text`
  * @param text The text to match.
  * @return true if this starts with the characters in `text`,
  * false otherwise
  * @stable ICU 2.0
  */
 inline UBool startsWith(const UnicodeString& text) const;

 /**
  * Determine if this starts with the characters in `srcText`
  * in the range [`srcStart`, `srcStart + srcLength`).
  * @param srcText The text to match.
  * @param srcStart the offset into `srcText` to start matching
  * @param srcLength the number of characters in `srcText` to match
  * @return true if this starts with the characters in `text`,
  * false otherwise
  * @stable ICU 2.0
  */
 inline UBool startsWith(const UnicodeString& srcText,
           int32_t srcStart,
           int32_t srcLength) const;

 /**
  * Determine if this starts with the characters in `srcChars`
  * @param srcChars The characters to match.
  * @param srcLength the number of characters in `srcChars`
  * @return true if this starts with the characters in `srcChars`,
  * false otherwise
  * @stable ICU 2.0
  */
 inline UBool startsWith(ConstChar16Ptr srcChars,
           int32_t srcLength) const;

 /**
  * Determine if this ends with the characters in `srcChars`
  * in the range  [`srcStart`, `srcStart + srcLength`).
  * @param srcChars The characters to match.
  * @param srcStart the offset into `srcText` to start matching
  * @param srcLength the number of characters in `srcChars` to match
  * @return true if this ends with the characters in `srcChars`, false otherwise
  * @stable ICU 2.0
  */
 inline UBool startsWith(const char16_t *srcChars,
           int32_t srcStart,
           int32_t srcLength) const;

 /**
  * Determine if this ends with the characters in `text`
  * @param text The text to match.
  * @return true if this ends with the characters in `text`,
  * false otherwise
  * @stable ICU 2.0
  */
 inline UBool endsWith(const UnicodeString& text) const;

 /**
  * Determine if this ends with the characters in `srcText`
  * in the range [`srcStart`, `srcStart + srcLength`).
  * @param srcText The text to match.
  * @param srcStart the offset into `srcText` to start matching
  * @param srcLength the number of characters in `srcText` to match
  * @return true if this ends with the characters in `text`,
  * false otherwise
  * @stable ICU 2.0
  */
 inline UBool endsWith(const UnicodeString& srcText,
         int32_t srcStart,
         int32_t srcLength) const;

 /**
  * Determine if this ends with the characters in `srcChars`
  * @param srcChars The characters to match.
  * @param srcLength the number of characters in `srcChars`
  * @return true if this ends with the characters in `srcChars`,
  * false otherwise
  * @stable ICU 2.0
  */
 inline UBool endsWith(ConstChar16Ptr srcChars,
         int32_t srcLength) const;

 /**
  * Determine if this ends with the characters in `srcChars`
  * in the range  [`srcStart`, `srcStart + srcLength`).
  * @param srcChars The characters to match.
  * @param srcStart the offset into `srcText` to start matching
  * @param srcLength the number of characters in `srcChars` to match
  * @return true if this ends with the characters in `srcChars`,
  * false otherwise
  * @stable ICU 2.0
  */
 inline UBool endsWith(const char16_t *srcChars,
         int32_t srcStart,
         int32_t srcLength) const;


 /* Searching - bitwise only */

 /**
  * Locate in this the first occurrence of the characters in `text`,
  * using bitwise comparison.
  * @param text The text to search for.
  * @return The offset into this of the start of `text`,
  * or -1 if not found.
  * @stable ICU 2.0
  */
 inline int32_t indexOf(const UnicodeString& text) const;

 /**
  * Locate in this the first occurrence of the characters in `text`
  * starting at offset `start`, using bitwise comparison.
  * @param text The text to search for.
  * @param start The offset at which searching will start.
  * @return The offset into this of the start of `text`,
  * or -1 if not found.
  * @stable ICU 2.0
  */
 inline int32_t indexOf(const UnicodeString& text,
             int32_t start) const;

 /**
  * Locate in this the first occurrence in the range
  * [`start`, `start + length`) of the characters
  * in `text`, using bitwise comparison.
  * @param text The text to search for.
  * @param start The offset at which searching will start.
  * @param length The number of characters to search
  * @return The offset into this of the start of `text`,
  * or -1 if not found.
  * @stable ICU 2.0
  */
 inline int32_t indexOf(const UnicodeString& text,
             int32_t start,
             int32_t length) const;

 /**
  * Locate in this the first occurrence in the range
  * [`start`, `start + length`) of the characters
  *  in `srcText` in the range
  * [`srcStart`, `srcStart + srcLength`),
  * using bitwise comparison.
  * @param srcText The text to search for.
  * @param srcStart the offset into `srcText` at which
  * to start matching
  * @param srcLength the number of characters in `srcText` to match
  * @param start the offset into this at which to start matching
  * @param length the number of characters in this to search
  * @return The offset into this of the start of `text`,
  * or -1 if not found.
  * @stable ICU 2.0
  */
 inline int32_t indexOf(const UnicodeString& srcText,
             int32_t srcStart,
             int32_t srcLength,
             int32_t start,
             int32_t length) const;

 /**
  * Locate in this the first occurrence of the characters in
  * `srcChars`
  * starting at offset `start`, using bitwise comparison.
  * @param srcChars The text to search for.
  * @param srcLength the number of characters in `srcChars` to match
  * @param start the offset into this at which to start matching
  * @return The offset into this of the start of `text`,
  * or -1 if not found.
  * @stable ICU 2.0
  */
 inline int32_t indexOf(const char16_t *srcChars,
             int32_t srcLength,
             int32_t start) const;

 /**
  * Locate in this the first occurrence in the range
  * [`start`, `start + length`) of the characters
  * in `srcChars`, using bitwise comparison.
  * @param srcChars The text to search for.
  * @param srcLength the number of characters in `srcChars`
  * @param start The offset at which searching will start.
  * @param length The number of characters to search
  * @return The offset into this of the start of `srcChars`,
  * or -1 if not found.
  * @stable ICU 2.0
  */
 inline int32_t indexOf(ConstChar16Ptr srcChars,
             int32_t srcLength,
             int32_t start,
             int32_t length) const;

 /**
  * Locate in this the first occurrence in the range
  * [`start`, `start + length`) of the characters
  * in `srcChars` in the range
  * [`srcStart`, `srcStart + srcLength`),
  * using bitwise comparison.
  * @param srcChars The text to search for.
  * @param srcStart the offset into `srcChars` at which
  * to start matching
  * @param srcLength the number of characters in `srcChars` to match
  * @param start the offset into this at which to start matching
  * @param length the number of characters in this to search
  * @return The offset into this of the start of `text`,
  * or -1 if not found.
  * @stable ICU 2.0
  */
 int32_t indexOf(const char16_t *srcChars,
             int32_t srcStart,
             int32_t srcLength,
             int32_t start,
             int32_t length) const;

 /**
  * Locate in this the first occurrence of the BMP code point `c`,
  * using bitwise comparison.
  * @param c The code unit to search for.
  * @return The offset into this of `c`, or -1 if not found.
  * @stable ICU 2.0
  */
 inline int32_t indexOf(char16_t c) const;

 /**
  * Locate in this the first occurrence of the code point `c`,
  * using bitwise comparison.
  *
  * @param c The code point to search for.
  * @return The offset into this of `c`, or -1 if not found.
  * @stable ICU 2.0
  */
 inline int32_t indexOf(UChar32 c) const;

 /**
  * Locate in this the first occurrence of the BMP code point `c`,
  * starting at offset `start`, using bitwise comparison.
  * @param c The code unit to search for.
  * @param start The offset at which searching will start.
  * @return The offset into this of `c`, or -1 if not found.
  * @stable ICU 2.0
  */
 inline int32_t indexOf(char16_t c,
             int32_t start) const;

 /**
  * Locate in this the first occurrence of the code point `c`
  * starting at offset `start`, using bitwise comparison.
  *
  * @param c The code point to search for.
  * @param start The offset at which searching will start.
  * @return The offset into this of `c`, or -1 if not found.
  * @stable ICU 2.0
  */
 inline int32_t indexOf(UChar32 c,
             int32_t start) const;

 /**
  * Locate in this the first occurrence of the BMP code point `c`
  * in the range [`start`, `start + length`),
  * using bitwise comparison.
  * @param c The code unit to search for.
  * @param start the offset into this at which to start matching
  * @param length the number of characters in this to search
  * @return The offset into this of `c`, or -1 if not found.
  * @stable ICU 2.0
  */
 inline int32_t indexOf(char16_t c,
             int32_t start,
             int32_t length) const;

 /**
  * Locate in this the first occurrence of the code point `c`
  * in the range [`start`, `start + length`),
  * using bitwise comparison.
  *
  * @param c The code point to search for.
  * @param start the offset into this at which to start matching
  * @param length the number of characters in this to search
  * @return The offset into this of `c`, or -1 if not found.
  * @stable ICU 2.0
  */
 inline int32_t indexOf(UChar32 c,
             int32_t start,
             int32_t length) const;

 /**
  * Locate in this the last occurrence of the characters in `text`,
  * using bitwise comparison.
  * @param text The text to search for.
  * @return The offset into this of the start of `text`,
  * or -1 if not found.
  * @stable ICU 2.0
  */
 inline int32_t lastIndexOf(const UnicodeString& text) const;

 /**
  * Locate in this the last occurrence of the characters in `text`
  * starting at offset `start`, using bitwise comparison.
  * @param text The text to search for.
  * @param start The offset at which searching will start.
  * @return The offset into this of the start of `text`,
  * or -1 if not found.
  * @stable ICU 2.0
  */
 inline int32_t lastIndexOf(const UnicodeString& text,
             int32_t start) const;

 /**
  * Locate in this the last occurrence in the range
  * [`start`, `start + length`) of the characters
  * in `text`, using bitwise comparison.
  * @param text The text to search for.
  * @param start The offset at which searching will start.
  * @param length The number of characters to search
  * @return The offset into this of the start of `text`,
  * or -1 if not found.
  * @stable ICU 2.0
  */
 inline int32_t lastIndexOf(const UnicodeString& text,
             int32_t start,
             int32_t length) const;

 /**
  * Locate in this the last occurrence in the range
  * [`start`, `start + length`) of the characters
  * in `srcText` in the range
  * [`srcStart`, `srcStart + srcLength`),
  * using bitwise comparison.
  * @param srcText The text to search for.
  * @param srcStart the offset into `srcText` at which
  * to start matching
  * @param srcLength the number of characters in `srcText` to match
  * @param start the offset into this at which to start matching
  * @param length the number of characters in this to search
  * @return The offset into this of the start of `text`,
  * or -1 if not found.
  * @stable ICU 2.0
  */
 inline int32_t lastIndexOf(const UnicodeString& srcText,
             int32_t srcStart,
             int32_t srcLength,
             int32_t start,
             int32_t length) const;

 /**
  * Locate in this the last occurrence of the characters in `srcChars`
  * starting at offset `start`, using bitwise comparison.
  * @param srcChars The text to search for.
  * @param srcLength the number of characters in `srcChars` to match
  * @param start the offset into this at which to start matching
  * @return The offset into this of the start of `text`,
  * or -1 if not found.
  * @stable ICU 2.0
  */
 inline int32_t lastIndexOf(const char16_t *srcChars,
             int32_t srcLength,
             int32_t start) const;

 /**
  * Locate in this the last occurrence in the range
  * [`start`, `start + length`) of the characters
  * in `srcChars`, using bitwise comparison.
  * @param srcChars The text to search for.
  * @param srcLength the number of characters in `srcChars`
  * @param start The offset at which searching will start.
  * @param length The number of characters to search
  * @return The offset into this of the start of `srcChars`,
  * or -1 if not found.
  * @stable ICU 2.0
  */
 inline int32_t lastIndexOf(ConstChar16Ptr srcChars,
             int32_t srcLength,
             int32_t start,
             int32_t length) const;

 /**
  * Locate in this the last occurrence in the range
  * [`start`, `start + length`) of the characters
  * in `srcChars` in the range
  * [`srcStart`, `srcStart + srcLength`),
  * using bitwise comparison.
  * @param srcChars The text to search for.
  * @param srcStart the offset into `srcChars` at which
  * to start matching
  * @param srcLength the number of characters in `srcChars` to match
  * @param start the offset into this at which to start matching
  * @param length the number of characters in this to search
  * @return The offset into this of the start of `text`,
  * or -1 if not found.
  * @stable ICU 2.0
  */
 int32_t lastIndexOf(const char16_t *srcChars,
             int32_t srcStart,
             int32_t srcLength,
             int32_t start,
             int32_t length) const;

 /**
  * Locate in this the last occurrence of the BMP code point `c`,
  * using bitwise comparison.
  * @param c The code unit to search for.
  * @return The offset into this of `c`, or -1 if not found.
  * @stable ICU 2.0
  */
 inline int32_t lastIndexOf(char16_t c) const;

 /**
  * Locate in this the last occurrence of the code point `c`,
  * using bitwise comparison.
  *
  * @param c The code point to search for.
  * @return The offset into this of `c`, or -1 if not found.
  * @stable ICU 2.0
  */
 inline int32_t lastIndexOf(UChar32 c) const;

 /**
  * Locate in this the last occurrence of the BMP code point `c`
  * starting at offset `start`, using bitwise comparison.
  * @param c The code unit to search for.
  * @param start The offset at which searching will start.
  * @return The offset into this of `c`, or -1 if not found.
  * @stable ICU 2.0
  */
 inline int32_t lastIndexOf(char16_t c,
             int32_t start) const;

 /**
  * Locate in this the last occurrence of the code point `c`
  * starting at offset `start`, using bitwise comparison.
  *
  * @param c The code point to search for.
  * @param start The offset at which searching will start.
  * @return The offset into this of `c`, or -1 if not found.
  * @stable ICU 2.0
  */
 inline int32_t lastIndexOf(UChar32 c,
             int32_t start) const;

 /**
  * Locate in this the last occurrence of the BMP code point `c`
  * in the range [`start`, `start + length`),
  * using bitwise comparison.
  * @param c The code unit to search for.
  * @param start the offset into this at which to start matching
  * @param length the number of characters in this to search
  * @return The offset into this of `c`, or -1 if not found.
  * @stable ICU 2.0
  */
 inline int32_t lastIndexOf(char16_t c,
             int32_t start,
             int32_t length) const;

 /**
  * Locate in this the last occurrence of the code point `c`
  * in the range [`start`, `start + length`),
  * using bitwise comparison.
  *
  * @param c The code point to search for.
  * @param start the offset into this at which to start matching
  * @param length the number of characters in this to search
  * @return The offset into this of `c`, or -1 if not found.
  * @stable ICU 2.0
  */
 inline int32_t lastIndexOf(UChar32 c,
             int32_t start,
             int32_t length) const;


 /* Character access */

 /**
  * Return the code unit at offset `offset`.
  * If the offset is not valid (0..length()-1) then U+ffff is returned.
  * @param offset a valid offset into the text
  * @return the code unit at offset `offset`
  *         or 0xffff if the offset is not valid for this string
  * @stable ICU 2.0
  */
 inline char16_t charAt(int32_t offset) const;

 /**
  * Return the code unit at offset `offset`.
  * If the offset is not valid (0..length()-1) then U+ffff is returned.
  * @param offset a valid offset into the text
  * @return the code unit at offset `offset`
  * @stable ICU 2.0
  */
 inline char16_t operator[] (int32_t offset) const;

 /**
  * Return the code point that contains the code unit
  * at offset `offset`.
  * If the offset is not valid (0..length()-1) then U+ffff is returned.
  * @param offset a valid offset into the text
  * that indicates the text offset of any of the code units
  * that will be assembled into a code point (21-bit value) and returned
  * @return the code point of text at `offset`
  *         or 0xffff if the offset is not valid for this string
  * @stable ICU 2.0
  */
 UChar32 char32At(int32_t offset) const;

 /**
  * Adjust a random-access offset so that
  * it points to the beginning of a Unicode character.
  * The offset that is passed in points to
  * any code unit of a code point,
  * while the returned offset will point to the first code unit
  * of the same code point.
  * In UTF-16, if the input offset points to a second surrogate
  * of a surrogate pair, then the returned offset will point
  * to the first surrogate.
  * @param offset a valid offset into one code point of the text
  * @return offset of the first code unit of the same code point
  * @see U16_SET_CP_START
  * @stable ICU 2.0
  */
 int32_t getChar32Start(int32_t offset) const;

 /**
  * Adjust a random-access offset so that
  * it points behind a Unicode character.
  * The offset that is passed in points behind
  * any code unit of a code point,
  * while the returned offset will point behind the last code unit
  * of the same code point.
  * In UTF-16, if the input offset points behind the first surrogate
  * (i.e., to the second surrogate)
  * of a surrogate pair, then the returned offset will point
  * behind the second surrogate (i.e., to the first surrogate).
  * @param offset a valid offset after any code unit of a code point of the text
  * @return offset of the first code unit after the same code point
  * @see U16_SET_CP_LIMIT
  * @stable ICU 2.0
  */
 int32_t getChar32Limit(int32_t offset) const;

 /**
  * Move the code unit index along the string by delta code points.
  * Interpret the input index as a code unit-based offset into the string,
  * move the index forward or backward by delta code points, and
  * return the resulting index.
  * The input index should point to the first code unit of a code point,
  * if there is more than one.
  *
  * Both input and output indexes are code unit-based as for all
  * string indexes/offsets in ICU (and other libraries, like MBCS char*).
  * If delta<0 then the index is moved backward (toward the start of the string).
  * If delta>0 then the index is moved forward (toward the end of the string).
  *
  * This behaves like CharacterIterator::move32(delta, kCurrent).
  *
  * Behavior for out-of-bounds indexes:
  * `moveIndex32` pins the input index to 0..length(), i.e.,
  * if the input index<0 then it is pinned to 0;
  * if it is index>length() then it is pinned to length().
  * Afterwards, the index is moved by `delta` code points
  * forward or backward,
  * but no further backward than to 0 and no further forward than to length().
  * The resulting index return value will be in between 0 and length(), inclusively.
  *
  * Examples:
  * \code
  *     // s has code points 'a' U+10000 'b' U+10ffff U+2029
  *     UnicodeString s(u"a\U00010000b\U0010ffff\u2029");
  *
  *     // initial index: position of U+10000
  *     int32_t index=1;
  *
  *     // the following examples will all result in index==4, position of U+10ffff
  *
  *     // skip 2 code points from some position in the string
  *     index=s.moveIndex32(index, 2); // skips U+10000 and 'b'
  *
  *     // go to the 3rd code point from the start of s (0-based)
  *     index=s.moveIndex32(0, 3); // skips 'a', U+10000, and 'b'
  *
  *     // go to the next-to-last code point of s
  *     index=s.moveIndex32(s.length(), -2); // backward-skips U+2029 and U+10ffff
  * \endcode
  *
  * @param index input code unit index
  * @param delta (signed) code point count to move the index forward or backward
  *        in the string
  * @return the resulting code unit index
  * @stable ICU 2.0
  */
 int32_t moveIndex32(int32_t index, int32_t delta) const;

 /* Substring extraction */

 /**
  * Copy the characters in the range
  * [`start`, `start + length`) into the array `dst`,
  * beginning at `dstStart`.
  * If the string aliases to `dst` itself as an external buffer,
  * then extract() will not copy the contents.
  *
  * @param start offset of first character which will be copied into the array
  * @param length the number of characters to extract
  * @param dst array in which to copy characters.  The length of `dst`
  * must be at least (`dstStart + length`).
  * @param dstStart the offset in `dst` where the first character
  * will be extracted
  * @stable ICU 2.0
  */
 inline void extract(int32_t start,
          int32_t length,
          Char16Ptr dst,
          int32_t dstStart = 0) const;

 /**
  * Copy the contents of the string into dest.
  * This is a convenience function that
  * checks if there is enough space in dest,
  * extracts the entire string if possible,
  * and NUL-terminates dest if possible.
  *
  * If the string fits into dest but cannot be NUL-terminated
  * (length()==destCapacity) then the error code is set to U_STRING_NOT_TERMINATED_WARNING.
  * If the string itself does not fit into dest
  * (length()>destCapacity) then the error code is set to U_BUFFER_OVERFLOW_ERROR.
  *
  * If the string aliases to `dest` itself as an external buffer,
  * then extract() will not copy the contents.
  *
  * @param dest Destination string buffer.
  * @param destCapacity Number of char16_ts available at dest.
  * @param errorCode ICU error code.
  * @return length()
  * @stable ICU 2.0
  */
 int32_t
 extract(Char16Ptr dest, int32_t destCapacity,
         UErrorCode &errorCode) const;

 /**
  * Copy the characters in the range
  * [`start`, `start + length`) into the  UnicodeString
  * `target`.
  * @param start offset of first character which will be copied
  * @param length the number of characters to extract
  * @param target UnicodeString into which to copy characters.
  * @stable ICU 2.0
  */
 inline void extract(int32_t start,
          int32_t length,
          UnicodeString& target) const;

 /**
  * Copy the characters in the range [`start`, `limit`)
  * into the array `dst`, beginning at `dstStart`.
  * @param start offset of first character which will be copied into the array
  * @param limit offset immediately following the last character to be copied
  * @param dst array in which to copy characters.  The length of `dst`
  * must be at least (`dstStart + (limit - start)`).
  * @param dstStart the offset in `dst` where the first character
  * will be extracted
  * @stable ICU 2.0
  */
 inline void extractBetween(int32_t start,
             int32_t limit,
             char16_t *dst,
             int32_t dstStart = 0) const;

 /**
  * Copy the characters in the range [`start`, `limit`)
  * into the UnicodeString `target`.  Replaceable API.
  * @param start offset of first character which will be copied
  * @param limit offset immediately following the last character to be copied
  * @param target UnicodeString into which to copy characters.
  * @stable ICU 2.0
  */
 virtual void extractBetween(int32_t start,
             int32_t limit,
             UnicodeString& target) const override;

 /**
  * Copy the characters in the range
  * [`start`, `start + startLength`) into an array of characters.
  * All characters must be invariant (see utypes.h).
  * Use US_INV as the last, signature-distinguishing parameter.
  *
  * This function does not write any more than `targetCapacity`
  * characters but returns the length of the entire output string
  * so that one can allocate a larger buffer and call the function again
  * if necessary.
  * The output string is NUL-terminated if possible.
  *
  * @param start offset of first character which will be copied
  * @param startLength the number of characters to extract
  * @param target the target buffer for extraction, can be nullptr
  *               if targetLength is 0
  * @param targetCapacity the length of the target buffer
  * @param inv Signature-distinguishing parameter, use US_INV.
  * @return the output string length, not including the terminating NUL
  * @stable ICU 3.2
  */
 int32_t extract(int32_t start,
          int32_t startLength,
          char *target,
          int32_t targetCapacity,
          enum EInvariant inv) const;

#if U_CHARSET_IS_UTF8 || !UCONFIG_NO_CONVERSION

 /**
  * Copy the characters in the range
  * [`start`, `start + length`) into an array of characters
  * in the platform's default codepage.
  * This function does not write any more than `targetLength`
  * characters but returns the length of the entire output string
  * so that one can allocate a larger buffer and call the function again
  * if necessary.
  * The output string is NUL-terminated if possible.
  *
  * @param start offset of first character which will be copied
  * @param startLength the number of characters to extract
  * @param target the target buffer for extraction
  * @param targetLength the length of the target buffer
  * If `target` is nullptr, then the number of bytes required for
  * `target` is returned.
  * @return the output string length, not including the terminating NUL
  * @stable ICU 2.0
  */
 int32_t extract(int32_t start,
          int32_t startLength,
          char *target,
          uint32_t targetLength) const;

#endif

#if !UCONFIG_NO_CONVERSION

 /**
  * Copy the characters in the range
  * [`start`, `start + length`) into an array of characters
  * in a specified codepage.
  * The output string is NUL-terminated.
  *
  * Recommendation: For invariant-character strings use
  * extract(int32_t start, int32_t length, char *target, int32_t targetCapacity, enum EInvariant inv) const
  * because it avoids object code dependencies of UnicodeString on
  * the conversion code.
  *
  * @param start offset of first character which will be copied
  * @param startLength the number of characters to extract
  * @param target the target buffer for extraction
  * @param codepage the desired codepage for the characters.  0 has
  * the special meaning of the default codepage
  * If `codepage` is an empty string (`""`),
  * then a simple conversion is performed on the codepage-invariant
  * subset ("invariant characters") of the platform encoding. See utypes.h.
  * If `target` is nullptr, then the number of bytes required for
  * `target` is returned. It is assumed that the target is big enough
  * to fit all of the characters.
  * @return the output string length, not including the terminating NUL
  * @stable ICU 2.0
  */
 inline int32_t extract(int32_t start,
                        int32_t startLength,
                        char* target,
                        const char* codepage = nullptr) const;

 /**
  * Copy the characters in the range
  * [`start`, `start + length`) into an array of characters
  * in a specified codepage.
  * This function does not write any more than `targetLength`
  * characters but returns the length of the entire output string
  * so that one can allocate a larger buffer and call the function again
  * if necessary.
  * The output string is NUL-terminated if possible.
  *
  * Recommendation: For invariant-character strings use
  * extract(int32_t start, int32_t length, char *target, int32_t targetCapacity, enum EInvariant inv) const
  * because it avoids object code dependencies of UnicodeString on
  * the conversion code.
  *
  * @param start offset of first character which will be copied
  * @param startLength the number of characters to extract
  * @param target the target buffer for extraction
  * @param targetLength the length of the target buffer
  * @param codepage the desired codepage for the characters.  0 has
  * the special meaning of the default codepage
  * If `codepage` is an empty string (`""`),
  * then a simple conversion is performed on the codepage-invariant
  * subset ("invariant characters") of the platform encoding. See utypes.h.
  * If `target` is nullptr, then the number of bytes required for
  * `target` is returned.
  * @return the output string length, not including the terminating NUL
  * @stable ICU 2.0
  */
 int32_t extract(int32_t start,
          int32_t startLength,
          char *target,
          uint32_t targetLength,
          const char *codepage) const;

 /**
  * Convert the UnicodeString into a codepage string using an existing UConverter.
  * The output string is NUL-terminated if possible.
  *
  * This function avoids the overhead of opening and closing a converter if
  * multiple strings are extracted.
  *
  * @param dest destination string buffer, can be nullptr if destCapacity==0
  * @param destCapacity the number of chars available at dest
  * @param cnv the converter object to be used (ucnv_resetFromUnicode() will be called),
  *        or nullptr for the default converter
  * @param errorCode normal ICU error code
  * @return the length of the output string, not counting the terminating NUL;
  *         if the length is greater than destCapacity, then the string will not fit
  *         and a buffer of the indicated length would need to be passed in
  * @stable ICU 2.0
  */
 int32_t extract(char *dest, int32_t destCapacity,
                 UConverter *cnv,
                 UErrorCode &errorCode) const;

#endif

 /**
  * Create a temporary substring for the specified range.
  * Unlike the substring constructor and setTo() functions,
  * the object returned here will be a read-only alias (using getBuffer())
  * rather than copying the text.
  * As a result, this substring operation is much faster but requires
  * that the original string not be modified or deleted during the lifetime
  * of the returned substring object.
  * @param start offset of the first character visible in the substring
  * @param length length of the substring
  * @return a read-only alias UnicodeString object for the substring
  * @stable ICU 4.4
  */
 UnicodeString tempSubString(int32_t start=0, int32_t length=INT32_MAX) const;

 /**
  * Create a temporary substring for the specified range.
  * Same as tempSubString(start, length) except that the substring range
  * is specified as a (start, limit) pair (with an exclusive limit index)
  * rather than a (start, length) pair.
  * @param start offset of the first character visible in the substring
  * @param limit offset immediately following the last character visible in the substring
  * @return a read-only alias UnicodeString object for the substring
  * @stable ICU 4.4
  */
 inline UnicodeString tempSubStringBetween(int32_t start, int32_t limit=INT32_MAX) const;

 /**
  * Convert the UnicodeString to UTF-8 and write the result
  * to a ByteSink. This is called by toUTF8String().
  * Unpaired surrogates are replaced with U+FFFD.
  * Calls u_strToUTF8WithSub().
  *
  * @param sink A ByteSink to which the UTF-8 version of the string is written.
  *             sink.Flush() is called at the end.
  * @stable ICU 4.2
  * @see toUTF8String
  */
 void toUTF8(ByteSink &sink) const;

 /**
  * Convert the UnicodeString to UTF-8 and append the result
  * to a standard string.
  * Unpaired surrogates are replaced with U+FFFD.
  * Calls toUTF8().
  *
  * @tparam StringClass A std::string or a std::u8string (or a compatible type)
  * @param result A std::string or a std::u8string (or a compatible object)
  *        to which the UTF-8 version of the string is appended.
  * @return The string object.
  * @stable ICU 4.2
  * @see toUTF8
  */
 template<typename StringClass>
 StringClass &toUTF8String(StringClass &result) const {
   StringByteSink<StringClass> sbs(&result, length());
   toUTF8(sbs);
   return result;
 }

#ifndef U_HIDE_DRAFT_API
 /**
  * Convert the UnicodeString to a UTF-8 string.
  * Unpaired surrogates are replaced with U+FFFD.
  * Calls toUTF8().
  *
  * @tparam StringClass A std::string or a std::u8string (or a compatible type)
  * @return A std::string or a std::u8string (or a compatible object)
  *        with the UTF-8 version of the string.
  * @draft ICU 78
  * @see toUTF8
  */
 template<typename StringClass>
 StringClass toUTF8String() const {
   StringClass result;
   StringByteSink<StringClass> sbs(&result, length());
   toUTF8(sbs);
   return result;
 }
#endif  // U_HIDE_DRAFT_API

 /**
  * Convert the UnicodeString to UTF-32.
  * Unpaired surrogates are replaced with U+FFFD.
  * Calls u_strToUTF32WithSub().
  *
  * @param utf32 destination string buffer, can be nullptr if capacity==0
  * @param capacity the number of UChar32s available at utf32
  * @param errorCode Standard ICU error code. Its input value must
  *                  pass the U_SUCCESS() test, or else the function returns
  *                  immediately. Check for U_FAILURE() on output or use with
  *                  function chaining. (See User Guide for details.)
  * @return The length of the UTF-32 string.
  * @see fromUTF32
  * @stable ICU 4.2
  */
 int32_t toUTF32(UChar32 *utf32, int32_t capacity, UErrorCode &errorCode) const;

 /* Length operations */

 /**
  * Return the length of the UnicodeString object.
  * The length is the number of char16_t code units are in the UnicodeString.
  * If you want the number of code points, please use countChar32().
  * @return the length of the UnicodeString object
  * @see countChar32
  * @stable ICU 2.0
  */
 inline int32_t length() const;

 /**
  * Count Unicode code points in the length char16_t code units of the string.
  * A code point may occupy either one or two char16_t code units.
  * Counting code points involves reading all code units.
  *
  * This functions is basically the inverse of moveIndex32().
  *
  * @param start the index of the first code unit to check
  * @param length the number of char16_t code units to check
  * @return the number of code points in the specified code units
  * @see length
  * @stable ICU 2.0
  */
 int32_t
 countChar32(int32_t start=0, int32_t length=INT32_MAX) const;

 /**
  * Check if the length char16_t code units of the string
  * contain more Unicode code points than a certain number.
  * This is more efficient than counting all code points in this part of the string
  * and comparing that number with a threshold.
  * This function may not need to scan the string at all if the length
  * falls within a certain range, and
  * never needs to count more than 'number+1' code points.
  * Logically equivalent to (countChar32(start, length)>number).
  * A Unicode code point may occupy either one or two char16_t code units.
  *
  * @param start the index of the first code unit to check (0 for the entire string)
  * @param length the number of char16_t code units to check
  *               (use INT32_MAX for the entire string; remember that start/length
  *                values are pinned)
  * @param number The number of code points in the (sub)string is compared against
  *               the 'number' parameter.
  * @return Boolean value for whether the string contains more Unicode code points
  *         than 'number'. Same as (u_countChar32(s, length)>number).
  * @see countChar32
  * @see u_strHasMoreChar32Than
  * @stable ICU 2.4
  */
 UBool
 hasMoreChar32Than(int32_t start, int32_t length, int32_t number) const;

 /**
  * Determine if this string is empty.
  * @return true if this string contains 0 characters, false otherwise.
  * @stable ICU 2.0
  */
 inline UBool isEmpty() const;

 /**
  * Return the capacity of the internal buffer of the UnicodeString object.
  * This is useful together with the getBuffer functions.
  * See there for details.
  *
  * @return the number of char16_ts available in the internal buffer
  * @see getBuffer
  * @stable ICU 2.0
  */
 inline int32_t getCapacity() const;

 /* Other operations */

 /**
  * Generate a hash code for this object.
  * @return The hash code of this UnicodeString.
  * @stable ICU 2.0
  */
 inline int32_t hashCode() const;

 /**
  * Determine if this object contains a valid string.
  * A bogus string has no value. It is different from an empty string,
  * although in both cases isEmpty() returns true and length() returns 0.
  * setToBogus() and isBogus() can be used to indicate that no string value is available.
  * For a bogus string, getBuffer() and getTerminatedBuffer() return nullptr, and
  * length() returns 0.
  *
  * @return true if the string is bogus/invalid, false otherwise
  * @see setToBogus()
  * @stable ICU 2.0
  */
 inline UBool isBogus() const;

#ifndef U_HIDE_DRAFT_API
private:
 // These type aliases are private; there is no guarantee that they will remain
 // aliases to the same types in subsequent versions of ICU.
 // Note that whether `std::u16string_view::const_iterator` is a pointer or a
 // class that models contiguous_iterator is platform-dependent.
 using unspecified_iterator = std::u16string_view::const_iterator;
 using unspecified_reverse_iterator = std::u16string_view::const_reverse_iterator;

public:
 /**
  * @return an iterator to the first code unit in this string.
  *     The iterator may be a pointer or a contiguous-iterator object.
  * @draft ICU 78
  */
 unspecified_iterator begin() const { return std::u16string_view(*this).begin(); }
 /**
  * @return an iterator to just past the last code unit in this string.
  *     The iterator may be a pointer or a contiguous-iterator object.
  * @draft ICU 78
  */
 unspecified_iterator end() const { return std::u16string_view(*this).end(); }
 /**
  * @return a reverse iterator to the last code unit in this string.
  *     The iterator may be a pointer or a contiguous-iterator object.
  * @draft ICU 78
  */
 unspecified_reverse_iterator rbegin() const { return std::u16string_view(*this).rbegin(); }
 /**
  * @return a reverse iterator to just before the first code unit in this string.
  *     The iterator may be a pointer or a contiguous-iterator object.
  * @draft ICU 78
  */
 unspecified_reverse_iterator rend() const { return std::u16string_view(*this).rend(); }
#endif  // U_HIDE_DRAFT_API

 //========================================
 // Write operations
 //========================================

 /* Assignment operations */

 /**
  * Assignment operator.  Replace the characters in this UnicodeString
  * with the characters from `srcText`.
  *
  * Starting with ICU 2.4, the assignment operator and the copy constructor
  * allocate a new buffer and copy the buffer contents even for readonly aliases.
  * By contrast, the fastCopyFrom() function implements the old,
  * more efficient but less safe behavior
  * of making this string also a readonly alias to the same buffer.
  *
  * If the source object has an "open" buffer from getBuffer(minCapacity),
  * then the copy is an empty string.
  *
  * @param srcText The text containing the characters to replace
  * @return a reference to this
  * @stable ICU 2.0
  * @see fastCopyFrom
  */
 UnicodeString &operator=(const UnicodeString &srcText);

 /**
  * Almost the same as the assignment operator.
  * Replace the characters in this UnicodeString
  * with the characters from `srcText`.
  *
  * This function works the same as the assignment operator
  * for all strings except for ones that are readonly aliases.
  *
  * Starting with ICU 2.4, the assignment operator and the copy constructor
  * allocate a new buffer and copy the buffer contents even for readonly aliases.
  * This function implements the old, more efficient but less safe behavior
  * of making this string also a readonly alias to the same buffer.
  *
  * The fastCopyFrom function must be used only if it is known that the lifetime of
  * this UnicodeString does not exceed the lifetime of the aliased buffer
  * including its contents, for example for strings from resource bundles
  * or aliases to string constants.
  *
  * If the source object has an "open" buffer from getBuffer(minCapacity),
  * then the copy is an empty string.
  *
  * @param src The text containing the characters to replace.
  * @return a reference to this
  * @stable ICU 2.4
  */
 UnicodeString &fastCopyFrom(const UnicodeString &src);

 /**
  * Assignment operator. Replaces the characters in this UnicodeString
  * with a copy of the characters from the `src`
  * which is, or which is implicitly convertible to,
  * a std::u16string_view or (if U_SIZEOF_WCHAR_T==2) std::wstring_view.
  *
  * @param src The string view containing the characters to copy.
  * @return a reference to this
  * @stable ICU 76
  */
 template<typename S, typename = std::enable_if_t<ConvertibleToU16StringView<S>>>
 inline UnicodeString &operator=(const S &src) {
   unBogus();
   return doReplace(0, length(), internal::toU16StringView(src));
 }

 /**
  * Move assignment operator; might leave src in bogus state.
  * This string will have the same contents and state that the source string had.
  * The behavior is undefined if *this and src are the same object.
  * @param src source string
  * @return *this
  * @stable ICU 56
  */
 UnicodeString &operator=(UnicodeString &&src) noexcept;

 /**
  * Swap strings.
  * @param other other string
  * @stable ICU 56
  */
 void swap(UnicodeString &other) noexcept;

 /**
  * Non-member UnicodeString swap function.
  * @param s1 will get s2's contents and state
  * @param s2 will get s1's contents and state
  * @stable ICU 56
  */
 friend inline void U_EXPORT2
 swap(UnicodeString &s1, UnicodeString &s2) noexcept {
   s1.swap(s2);
 }

 /**
  * Assignment operator.  Replace the characters in this UnicodeString
  * with the code unit `ch`.
  * @param ch the code unit to replace
  * @return a reference to this
  * @stable ICU 2.0
  */
 inline UnicodeString& operator= (char16_t ch);

 /**
  * Assignment operator.  Replace the characters in this UnicodeString
  * with the code point `ch`.
  * @param ch the code point to replace
  * @return a reference to this
  * @stable ICU 2.0
  */
 inline UnicodeString& operator= (UChar32 ch);

 /**
  * Set the text in the UnicodeString object to the characters
  * in `srcText` in the range
  * [`srcStart`, `srcText.length()`).
  * `srcText` is not modified.
  * @param srcText the source for the new characters
  * @param srcStart the offset into `srcText` where new characters
  * will be obtained
  * @return a reference to this
  * @stable ICU 2.2
  */
 inline UnicodeString& setTo(const UnicodeString& srcText,
              int32_t srcStart);

 /**
  * Set the text in the UnicodeString object to the characters
  * in `srcText` in the range
  * [`srcStart`, `srcStart + srcLength`).
  * `srcText` is not modified.
  * @param srcText the source for the new characters
  * @param srcStart the offset into `srcText` where new characters
  * will be obtained
  * @param srcLength the number of characters in `srcText` in the
  * replace string.
  * @return a reference to this
  * @stable ICU 2.0
  */
 inline UnicodeString& setTo(const UnicodeString& srcText,
              int32_t srcStart,
              int32_t srcLength);

 /**
  * Set the text in the UnicodeString object to the characters in
  * `srcText`.
  * `srcText` is not modified.
  * @param srcText the source for the new characters
  * @return a reference to this
  * @stable ICU 2.0
  */
 inline UnicodeString& setTo(const UnicodeString& srcText);

 /**
  * Set the characters in the UnicodeString object to the characters
  * in `srcChars`. `srcChars` is not modified.
  * @param srcChars the source for the new characters
  * @param srcLength the number of Unicode characters in srcChars.
  * @return a reference to this
  * @stable ICU 2.0
  */
 inline UnicodeString& setTo(const char16_t *srcChars,
              int32_t srcLength);

 /**
  * Set the characters in the UnicodeString object to the code unit
  * `srcChar`.
  * @param srcChar the code unit which becomes the UnicodeString's character
  * content
  * @return a reference to this
  * @stable ICU 2.0
  */
 inline UnicodeString& setTo(char16_t srcChar);

 /**
  * Set the characters in the UnicodeString object to the code point
  * `srcChar`.
  * @param srcChar the code point which becomes the UnicodeString's character
  * content
  * @return a reference to this
  * @stable ICU 2.0
  */
 inline UnicodeString& setTo(UChar32 srcChar);

 /**
  * Aliasing setTo() function, analogous to the readonly-aliasing char16_t* constructor.
  * The text will be used for the UnicodeString object, but
  * it will not be released when the UnicodeString is destroyed.
  * This has copy-on-write semantics:
  * When the string is modified, then the buffer is first copied into
  * newly allocated memory.
  * The aliased buffer is never modified.
  *
  * In an assignment to another UnicodeString, when using the copy constructor
  * or the assignment operator, the text will be copied.
  * When using fastCopyFrom(), the text will be aliased again,
  * so that both strings then alias the same readonly-text.
  *
  * @param isTerminated specifies if `text` is `NUL`-terminated.
  *                     This must be true if `textLength==-1`.
  * @param text The characters to alias for the UnicodeString.
  * @param textLength The number of Unicode characters in `text` to alias.
  *                   If -1, then this constructor will determine the length
  *                   by calling `u_strlen()`.
  * @return a reference to this
  * @stable ICU 2.0
  */
 UnicodeString &setTo(UBool isTerminated,
                      ConstChar16Ptr text,
                      int32_t textLength);

 /**
  * Aliasing setTo() function, analogous to the writable-aliasing char16_t* constructor.
  * The text will be used for the UnicodeString object, but
  * it will not be released when the UnicodeString is destroyed.
  * This has write-through semantics:
  * For as long as the capacity of the buffer is sufficient, write operations
  * will directly affect the buffer. When more capacity is necessary, then
  * a new buffer will be allocated and the contents copied as with regularly
  * constructed strings.
  * In an assignment to another UnicodeString, the buffer will be copied.
  * The extract(Char16Ptr dst) function detects whether the dst pointer is the same
  * as the string buffer itself and will in this case not copy the contents.
  *
  * @param buffer The characters to alias for the UnicodeString.
  * @param buffLength The number of Unicode characters in `buffer` to alias.
  * @param buffCapacity The size of `buffer` in char16_ts.
  * @return a reference to this
  * @stable ICU 2.0
  */
 UnicodeString &setTo(char16_t *buffer,
                      int32_t buffLength,
                      int32_t buffCapacity);

 /**
  * Make this UnicodeString object invalid.
  * The string will test true with isBogus().
  *
  * A bogus string has no value. It is different from an empty string.
  * It can be used to indicate that no string value is available.
  * getBuffer() and getTerminatedBuffer() return nullptr, and
  * length() returns 0.
  *
  * This utility function is used throughout the UnicodeString
  * implementation to indicate that a UnicodeString operation failed,
  * and may be used in other functions,
  * especially but not exclusively when such functions do not
  * take a UErrorCode for simplicity.
  *
  * The following methods, and no others, will clear a string object's bogus flag:
  * - remove()
  * - remove(0, INT32_MAX)
  * - truncate(0)
  * - operator=() (assignment operator)
  * - setTo(...)
  *
  * The simplest ways to turn a bogus string into an empty one
  * is to use the remove() function.
  * Examples for other functions that are equivalent to "set to empty string":
  * \code
  * if(s.isBogus()) {
  *   s.remove();           // set to an empty string (remove all), or
  *   s.remove(0, INT32_MAX); // set to an empty string (remove all), or
  *   s.truncate(0);        // set to an empty string (complete truncation), or
  *   s=UnicodeString();    // assign an empty string, or
  *   s.setTo((UChar32)-1); // set to a pseudo code point that is out of range, or
  *   s.setTo(u"", 0);      // set to an empty C Unicode string
  * }
  * \endcode
  *
  * @see isBogus()
  * @stable ICU 2.0
  */
 void setToBogus();

 /**
  * Set the character at the specified offset to the specified character.
  * @param offset A valid offset into the text of the character to set
  * @param ch The new character
  * @return A reference to this
  * @stable ICU 2.0
  */
 UnicodeString& setCharAt(int32_t offset,
              char16_t ch);


 /* Append operations */

 /**
  * Append operator. Append the code unit `ch` to the UnicodeString
  * object.
  * @param ch the code unit to be appended
  * @return a reference to this
  * @stable ICU 2.0
  */
inline  UnicodeString& operator+= (char16_t ch);

 /**
  * Append operator. Append the code point `ch` to the UnicodeString
  * object.
  * @param ch the code point to be appended
  * @return a reference to this
  * @stable ICU 2.0
  */
inline  UnicodeString& operator+= (UChar32 ch);

 /**
  * Append operator. Append the characters in `srcText` to the
  * UnicodeString object. `srcText` is not modified.
  * @param srcText the source for the new characters
  * @return a reference to this
  * @stable ICU 2.0
  */
 inline UnicodeString& operator+= (const UnicodeString& srcText);

 /**
  * Append operator. Appends the characters in `src`
  * which is, or which is implicitly convertible to,
  * a std::u16string_view or (if U_SIZEOF_WCHAR_T==2) std::wstring_view,
  * to the UnicodeString object.
  *
  * @param src the source for the new characters
  * @return a reference to this
  * @stable ICU 76
  */
 template<typename S, typename = std::enable_if_t<ConvertibleToU16StringView<S>>>
 inline UnicodeString& operator+=(const S &src) {
   return doAppend(internal::toU16StringView(src));
 }

 /**
  * Append the characters
  * in `srcText` in the range
  * [`srcStart`, `srcStart + srcLength`) to the
  * UnicodeString object at offset `start`. `srcText`
  * is not modified.
  * @param srcText the source for the new characters
  * @param srcStart the offset into `srcText` where new characters
  * will be obtained
  * @param srcLength the number of characters in `srcText` in
  * the append string
  * @return a reference to this
  * @stable ICU 2.0
  */
 inline UnicodeString& append(const UnicodeString& srcText,
           int32_t srcStart,
           int32_t srcLength);

 /**
  * Append the characters in `srcText` to the UnicodeString object.
  * `srcText` is not modified.
  * @param srcText the source for the new characters
  * @return a reference to this
  * @stable ICU 2.0
  */
 inline UnicodeString& append(const UnicodeString& srcText);

 /**
  * Append the characters in `srcChars` in the range
  * [`srcStart`, `srcStart + srcLength`) to the UnicodeString
  * object at offset
  * `start`. `srcChars` is not modified.
  * @param srcChars the source for the new characters
  * @param srcStart the offset into `srcChars` where new characters
  * will be obtained
  * @param srcLength the number of characters in `srcChars` in
  *                  the append string; can be -1 if `srcChars` is NUL-terminated
  * @return a reference to this
  * @stable ICU 2.0
  */
 inline UnicodeString& append(const char16_t *srcChars,
           int32_t srcStart,
           int32_t srcLength);

 /**
  * Append the characters in `srcChars` to the UnicodeString object.
  * `srcChars` is not modified.
  * @param srcChars the source for the new characters
  * @param srcLength the number of Unicode characters in `srcChars`;
  *                  can be -1 if `srcChars` is NUL-terminated
  * @return a reference to this
  * @stable ICU 2.0
  */
 inline UnicodeString& append(ConstChar16Ptr srcChars,
           int32_t srcLength);

 /**
  * Appends the characters in `src`
  * which is, or which is implicitly convertible to,
  * a std::u16string_view or (if U_SIZEOF_WCHAR_T==2) std::wstring_view,
  * to the UnicodeString object.
  *
  * @param src the source for the new characters
  * @return a reference to this
  * @stable ICU 76
  */
 template<typename S, typename = std::enable_if_t<ConvertibleToU16StringView<S>>>
 inline UnicodeString& append(const S &src) {
   return doAppend(internal::toU16StringView(src));
 }

 /**
  * Append the code unit `srcChar` to the UnicodeString object.
  * @param srcChar the code unit to append
  * @return a reference to this
  * @stable ICU 2.0
  */
 inline UnicodeString& append(char16_t srcChar);

 /**
  * Append the code point `srcChar` to the UnicodeString object.
  * @param srcChar the code point to append
  * @return a reference to this
  * @stable ICU 2.0
  */
 UnicodeString& append(UChar32 srcChar);

#ifndef U_HIDE_DRAFT_API
 /**
  * Appends the code unit `c` to the UnicodeString object.
  * Same as append(c) except does not return *this.
  *
  * @param c the code unit to append
  * @draft ICU 78
  */
 inline void push_back(char16_t c) { append(c); }
#endif  // U_HIDE_DRAFT_API

 /* Insert operations */

 /**
  * Insert the characters in `srcText` in the range
  * [`srcStart`, `srcStart + srcLength`) into the UnicodeString
  * object at offset `start`. `srcText` is not modified.
  * @param start the offset where the insertion begins
  * @param srcText the source for the new characters
  * @param srcStart the offset into `srcText` where new characters
  * will be obtained
  * @param srcLength the number of characters in `srcText` in
  * the insert string
  * @return a reference to this
  * @stable ICU 2.0
  */
 inline UnicodeString& insert(int32_t start,
           const UnicodeString& srcText,
           int32_t srcStart,
           int32_t srcLength);

 /**
  * Insert the characters in `srcText` into the UnicodeString object
  * at offset `start`. `srcText` is not modified.
  * @param start the offset where the insertion begins
  * @param srcText the source for the new characters
  * @return a reference to this
  * @stable ICU 2.0
  */
 inline UnicodeString& insert(int32_t start,
           const UnicodeString& srcText);

 /**
  * Insert the characters in `srcChars` in the range
  * [`srcStart`, `srcStart + srcLength`) into the UnicodeString
  *  object at offset `start`. `srcChars` is not modified.
  * @param start the offset at which the insertion begins
  * @param srcChars the source for the new characters
  * @param srcStart the offset into `srcChars` where new characters
  * will be obtained
  * @param srcLength the number of characters in `srcChars`
  * in the insert string
  * @return a reference to this
  * @stable ICU 2.0
  */
 inline UnicodeString& insert(int32_t start,
           const char16_t *srcChars,
           int32_t srcStart,
           int32_t srcLength);

 /**
  * Insert the characters in `srcChars` into the UnicodeString object
  * at offset `start`. `srcChars` is not modified.
  * @param start the offset where the insertion begins
  * @param srcChars the source for the new characters
  * @param srcLength the number of Unicode characters in srcChars.
  * @return a reference to this
  * @stable ICU 2.0
  */
 inline UnicodeString& insert(int32_t start,
           ConstChar16Ptr srcChars,
           int32_t srcLength);

 /**
  * Insert the code unit `srcChar` into the UnicodeString object at
  * offset `start`.
  * @param start the offset at which the insertion occurs
  * @param srcChar the code unit to insert
  * @return a reference to this
  * @stable ICU 2.0
  */
 inline UnicodeString& insert(int32_t start,
           char16_t srcChar);

 /**
  * Insert the code point `srcChar` into the UnicodeString object at
  * offset `start`.
  * @param start the offset at which the insertion occurs
  * @param srcChar the code point to insert
  * @return a reference to this
  * @stable ICU 2.0
  */
 inline UnicodeString& insert(int32_t start,
           UChar32 srcChar);


 /* Replace operations */

 /**
  * Replace the characters in the range
  * [`start`, `start + length`) with the characters in
  * `srcText` in the range
  * [`srcStart`, `srcStart + srcLength`).
  * `srcText` is not modified.
  * @param start the offset at which the replace operation begins
  * @param length the number of characters to replace. The character at
  * `start + length` is not modified.
  * @param srcText the source for the new characters
  * @param srcStart the offset into `srcText` where new characters
  * will be obtained
  * @param srcLength the number of characters in `srcText` in
  * the replace string
  * @return a reference to this
  * @stable ICU 2.0
  */
 inline UnicodeString& replace(int32_t start,
            int32_t length,
            const UnicodeString& srcText,
            int32_t srcStart,
            int32_t srcLength);

 /**
  * Replace the characters in the range
  * [`start`, `start + length`)
  * with the characters in `srcText`.  `srcText` is
  *  not modified.
  * @param start the offset at which the replace operation begins
  * @param length the number of characters to replace. The character at
  * `start + length` is not modified.
  * @param srcText the source for the new characters
  * @return a reference to this
  * @stable ICU 2.0
  */
 inline UnicodeString& replace(int32_t start,
            int32_t length,
            const UnicodeString& srcText);

 /**
  * Replace the characters in the range
  * [`start`, `start + length`) with the characters in
  * `srcChars` in the range
  * [`srcStart`, `srcStart + srcLength`). `srcChars`
  * is not modified.
  * @param start the offset at which the replace operation begins
  * @param length the number of characters to replace.  The character at
  * `start + length` is not modified.
  * @param srcChars the source for the new characters
  * @param srcStart the offset into `srcChars` where new characters
  * will be obtained
  * @param srcLength the number of characters in `srcChars`
  * in the replace string
  * @return a reference to this
  * @stable ICU 2.0
  */
 inline UnicodeString& replace(int32_t start,
            int32_t length,
            const char16_t *srcChars,
            int32_t srcStart,
            int32_t srcLength);

 /**
  * Replace the characters in the range
  * [`start`, `start + length`) with the characters in
  * `srcChars`.  `srcChars` is not modified.
  * @param start the offset at which the replace operation begins
  * @param length number of characters to replace.  The character at
  * `start + length` is not modified.
  * @param srcChars the source for the new characters
  * @param srcLength the number of Unicode characters in srcChars
  * @return a reference to this
  * @stable ICU 2.0
  */
 inline UnicodeString& replace(int32_t start,
            int32_t length,
            ConstChar16Ptr srcChars,
            int32_t srcLength);

 /**
  * Replace the characters in the range
  * [`start`, `start + length`) with the code unit
  * `srcChar`.
  * @param start the offset at which the replace operation begins
  * @param length the number of characters to replace.  The character at
  * `start + length` is not modified.
  * @param srcChar the new code unit
  * @return a reference to this
  * @stable ICU 2.0
  */
 inline UnicodeString& replace(int32_t start,
            int32_t length,
            char16_t srcChar);

 /**
  * Replace the characters in the range
  * [`start`, `start + length`) with the code point
  * `srcChar`.
  * @param start the offset at which the replace operation begins
  * @param length the number of characters to replace.  The character at
  * `start + length` is not modified.
  * @param srcChar the new code point
  * @return a reference to this
  * @stable ICU 2.0
  */
 UnicodeString& replace(int32_t start, int32_t length, UChar32 srcChar);

 /**
  * Replace the characters in the range [`start`, `limit`)
  * with the characters in `srcText`. `srcText` is not modified.
  * @param start the offset at which the replace operation begins
  * @param limit the offset immediately following the replace range
  * @param srcText the source for the new characters
  * @return a reference to this
  * @stable ICU 2.0
  */
 inline UnicodeString& replaceBetween(int32_t start,
               int32_t limit,
               const UnicodeString& srcText);

 /**
  * Replace the characters in the range [`start`, `limit`)
  * with the characters in `srcText` in the range
  * [`srcStart`, `srcLimit`). `srcText` is not modified.
  * @param start the offset at which the replace operation begins
  * @param limit the offset immediately following the replace range
  * @param srcText the source for the new characters
  * @param srcStart the offset into `srcChars` where new characters
  * will be obtained
  * @param srcLimit the offset immediately following the range to copy
  * in `srcText`
  * @return a reference to this
  * @stable ICU 2.0
  */
 inline UnicodeString& replaceBetween(int32_t start,
               int32_t limit,
               const UnicodeString& srcText,
               int32_t srcStart,
               int32_t srcLimit);

 /**
  * Replace a substring of this object with the given text.
  * @param start the beginning index, inclusive; `0 <= start <= limit`.
  * @param limit the ending index, exclusive; `start <= limit <= length()`.
  * @param text the text to replace characters `start` to `limit - 1`
  * @stable ICU 2.0
  */
 virtual void handleReplaceBetween(int32_t start,
                                   int32_t limit,
                                   const UnicodeString& text) override;

 /**
  * Replaceable API
  * @return true if it has MetaData
  * @stable ICU 2.4
  */
 virtual UBool hasMetaData() const override;

 /**
  * Copy a substring of this object, retaining attribute (out-of-band)
  * information.  This method is used to duplicate or reorder substrings.
  * The destination index must not overlap the source range.
  *
  * @param start the beginning index, inclusive; `0 <= start <= limit`.
  * @param limit the ending index, exclusive; `start <= limit <= length()`.
  * @param dest the destination index.  The characters from
  *             `start..limit-1` will be copied to `dest`.
  * Implementations of this method may assume that `dest <= start ||
  * dest >= limit`.
  * @stable ICU 2.0
  */
 virtual void copy(int32_t start, int32_t limit, int32_t dest) override;

 /* Search and replace operations */

 /**
  * Replace all occurrences of characters in oldText with the characters
  * in newText
  * @param oldText the text containing the search text
  * @param newText the text containing the replacement text
  * @return a reference to this
  * @stable ICU 2.0
  */
 inline UnicodeString& findAndReplace(const UnicodeString& oldText,
               const UnicodeString& newText);

 /**
  * Replace all occurrences of characters in oldText with characters
  * in newText
  * in the range [`start`, `start + length`).
  * @param start the start of the range in which replace will performed
  * @param length the length of the range in which replace will be performed
  * @param oldText the text containing the search text
  * @param newText the text containing the replacement text
  * @return a reference to this
  * @stable ICU 2.0
  */
 inline UnicodeString& findAndReplace(int32_t start,
               int32_t length,
               const UnicodeString& oldText,
               const UnicodeString& newText);

 /**
  * Replace all occurrences of characters in oldText in the range
  * [`oldStart`, `oldStart + oldLength`) with the characters
  * in newText in the range
  * [`newStart`, `newStart + newLength`)
  * in the range [`start`, `start + length`).
  * @param start the start of the range in which replace will performed
  * @param length the length of the range in which replace will be performed
  * @param oldText the text containing the search text
  * @param oldStart the start of the search range in `oldText`
  * @param oldLength the length of the search range in `oldText`
  * @param newText the text containing the replacement text
  * @param newStart the start of the replacement range in `newText`
  * @param newLength the length of the replacement range in `newText`
  * @return a reference to this
  * @stable ICU 2.0
  */
 UnicodeString& findAndReplace(int32_t start,
               int32_t length,
               const UnicodeString& oldText,
               int32_t oldStart,
               int32_t oldLength,
               const UnicodeString& newText,
               int32_t newStart,
               int32_t newLength);


 /* Remove operations */

 /**
  * Removes all characters from the UnicodeString object and clears the bogus flag.
  * This is the UnicodeString equivalent of std::string’s clear().
  *
  * @return a reference to this
  * @see setToBogus
  * @stable ICU 2.0
  */
 inline UnicodeString& remove();

 /**
  * Remove the characters in the range
  * [`start`, `start + length`) from the UnicodeString object.
  * @param start the offset of the first character to remove
  * @param length the number of characters to remove
  * @return a reference to this
  * @stable ICU 2.0
  */
 inline UnicodeString& remove(int32_t start,
                              int32_t length = static_cast<int32_t>(INT32_MAX));

 /**
  * Remove the characters in the range
  * [`start`, `limit`) from the UnicodeString object.
  * @param start the offset of the first character to remove
  * @param limit the offset immediately following the range to remove
  * @return a reference to this
  * @stable ICU 2.0
  */
 inline UnicodeString& removeBetween(int32_t start,
                                     int32_t limit = static_cast<int32_t>(INT32_MAX));

 /**
  * Retain only the characters in the range
  * [`start`, `limit`) from the UnicodeString object.
  * Removes characters before `start` and at and after `limit`.
  * @param start the offset of the first character to retain
  * @param limit the offset immediately following the range to retain
  * @return a reference to this
  * @stable ICU 4.4
  */
 inline UnicodeString &retainBetween(int32_t start, int32_t limit = INT32_MAX);

 /* Length operations */

 /**
  * Pad the start of this UnicodeString with the character `padChar`.
  * If the length of this UnicodeString is less than targetLength,
  * length() - targetLength copies of padChar will be added to the
  * beginning of this UnicodeString.
  * @param targetLength the desired length of the string
  * @param padChar the character to use for padding. Defaults to
  * space (U+0020)
  * @return true if the text was padded, false otherwise.
  * @stable ICU 2.0
  */
 UBool padLeading(int32_t targetLength,
                   char16_t padChar = 0x0020);

 /**
  * Pad the end of this UnicodeString with the character `padChar`.
  * If the length of this UnicodeString is less than targetLength,
  * length() - targetLength copies of padChar will be added to the
  * end of this UnicodeString.
  * @param targetLength the desired length of the string
  * @param padChar the character to use for padding. Defaults to
  * space (U+0020)
  * @return true if the text was padded, false otherwise.
  * @stable ICU 2.0
  */
 UBool padTrailing(int32_t targetLength,
                    char16_t padChar = 0x0020);

 /**
  * Truncate this UnicodeString to the `targetLength`.
  * @param targetLength the desired length of this UnicodeString.
  * @return true if the text was truncated, false otherwise
  * @stable ICU 2.0
  */
 inline UBool truncate(int32_t targetLength);

 /**
  * Trims leading and trailing whitespace from this UnicodeString.
  * @return a reference to this
  * @stable ICU 2.0
  */
 UnicodeString& trim();

 /* Miscellaneous operations */

 /**
  * Reverse this UnicodeString in place.
  * @return a reference to this
  * @stable ICU 2.0
  */
 inline UnicodeString& reverse();

 /**
  * Reverse the range [`start`, `start + length`) in
  * this UnicodeString.
  * @param start the start of the range to reverse
  * @param length the number of characters to to reverse
  * @return a reference to this
  * @stable ICU 2.0
  */
 inline UnicodeString& reverse(int32_t start,
            int32_t length);

 /**
  * Convert the characters in this to UPPER CASE following the conventions of
  * the default locale.
  * @return A reference to this.
  * @stable ICU 2.0
  */
 UnicodeString& toUpper();

 /**
  * Convert the characters in this to UPPER CASE following the conventions of
  * a specific locale.
  * @param locale The locale containing the conventions to use.
  * @return A reference to this.
  * @stable ICU 2.0
  */
 UnicodeString& toUpper(const Locale& locale);

 /**
  * Convert the characters in this to lower case following the conventions of
  * the default locale.
  * @return A reference to this.
  * @stable ICU 2.0
  */
 UnicodeString& toLower();

 /**
  * Convert the characters in this to lower case following the conventions of
  * a specific locale.
  * @param locale The locale containing the conventions to use.
  * @return A reference to this.
  * @stable ICU 2.0
  */
 UnicodeString& toLower(const Locale& locale);

#if !UCONFIG_NO_BREAK_ITERATION

 /**
  * Titlecase this string, convenience function using the default locale.
  *
  * Casing is locale-dependent and context-sensitive.
  * Titlecasing uses a break iterator to find the first characters of words
  * that are to be titlecased. It titlecases those characters and lowercases
  * all others.
  *
  * The titlecase break iterator can be provided to customize for arbitrary
  * styles, using rules and dictionaries beyond the standard iterators.
  * It may be more efficient to always provide an iterator to avoid
  * opening and closing one for each string.
  * If the break iterator passed in is null, the default Unicode algorithm
  * will be used to determine the titlecase positions.
  *
  * This function uses only the setText(), first() and next() methods of the
  * provided break iterator.
  *
  * @param titleIter A break iterator to find the first characters of words
  *                  that are to be titlecased.
  *                  If none is provided (0), then a standard titlecase
  *                  break iterator is opened.
  *                  Otherwise the provided iterator is set to the string's text.
  * @return A reference to this.
  * @stable ICU 2.1
  */
 UnicodeString &toTitle(BreakIterator *titleIter);

 /**
  * Titlecase this string.
  *
  * Casing is locale-dependent and context-sensitive.
  * Titlecasing uses a break iterator to find the first characters of words
  * that are to be titlecased. It titlecases those characters and lowercases
  * all others.
  *
  * The titlecase break iterator can be provided to customize for arbitrary
  * styles, using rules and dictionaries beyond the standard iterators.
  * It may be more efficient to always provide an iterator to avoid
  * opening and closing one for each string.
  * If the break iterator passed in is null, the default Unicode algorithm
  * will be used to determine the titlecase positions.
  *
  * This function uses only the setText(), first() and next() methods of the
  * provided break iterator.
  *
  * @param titleIter A break iterator to find the first characters of words
  *                  that are to be titlecased.
  *                  If none is provided (0), then a standard titlecase
  *                  break iterator is opened.
  *                  Otherwise the provided iterator is set to the string's text.
  * @param locale    The locale to consider.
  * @return A reference to this.
  * @stable ICU 2.1
  */
 UnicodeString &toTitle(BreakIterator *titleIter, const Locale &locale);

 /**
  * Titlecase this string, with options.
  *
  * Casing is locale-dependent and context-sensitive.
  * Titlecasing uses a break iterator to find the first characters of words
  * that are to be titlecased. It titlecases those characters and lowercases
  * all others. (This can be modified with options.)
  *
  * The titlecase break iterator can be provided to customize for arbitrary
  * styles, using rules and dictionaries beyond the standard iterators.
  * It may be more efficient to always provide an iterator to avoid
  * opening and closing one for each string.
  * If the break iterator passed in is null, the default Unicode algorithm
  * will be used to determine the titlecase positions.
  *
  * This function uses only the setText(), first() and next() methods of the
  * provided break iterator.
  *
  * @param titleIter A break iterator to find the first characters of words
  *                  that are to be titlecased.
  *                  If none is provided (0), then a standard titlecase
  *                  break iterator is opened.
  *                  Otherwise the provided iterator is set to the string's text.
  * @param locale    The locale to consider.
  * @param options   Options bit set, usually 0. See U_TITLECASE_NO_LOWERCASE,
  *                  U_TITLECASE_NO_BREAK_ADJUSTMENT, U_TITLECASE_ADJUST_TO_CASED,
  *                  U_TITLECASE_WHOLE_STRING, U_TITLECASE_SENTENCES.
  * @return A reference to this.
  * @stable ICU 3.8
  */
 UnicodeString &toTitle(BreakIterator *titleIter, const Locale &locale, uint32_t options);

#endif

 /**
  * Case-folds the characters in this string.
  *
  * Case-folding is locale-independent and not context-sensitive,
  * but there is an option for whether to include or exclude mappings for dotted I
  * and dotless i that are marked with 'T' in CaseFolding.txt.
  *
  * The result may be longer or shorter than the original.
  *
  * @param options Either U_FOLD_CASE_DEFAULT or U_FOLD_CASE_EXCLUDE_SPECIAL_I
  * @return A reference to this.
  * @stable ICU 2.0
  */
 UnicodeString &foldCase(uint32_t options=0 /*U_FOLD_CASE_DEFAULT*/);

 //========================================
 // Access to the internal buffer
 //========================================

 /**
  * Get a read/write pointer to the internal buffer.
  * The buffer is guaranteed to be large enough for at least minCapacity char16_ts,
  * writable, and is still owned by the UnicodeString object.
  * Calls to getBuffer(minCapacity) must not be nested, and
  * must be matched with calls to releaseBuffer(newLength).
  * If the string buffer was read-only or shared,
  * then it will be reallocated and copied.
  *
  * An attempted nested call will return 0, and will not further modify the
  * state of the UnicodeString object.
  * It also returns 0 if the string is bogus.
  *
  * The actual capacity of the string buffer may be larger than minCapacity.
  * getCapacity() returns the actual capacity.
  * For many operations, the full capacity should be used to avoid reallocations.
  *
  * While the buffer is "open" between getBuffer(minCapacity)
  * and releaseBuffer(newLength), the following applies:
  * - The string length is set to 0.
  * - Any read API call on the UnicodeString object will behave like on a 0-length string.
  * - Any write API call on the UnicodeString object is disallowed and will have no effect.
  * - You can read from and write to the returned buffer.
  * - The previous string contents will still be in the buffer;
  *   if you want to use it, then you need to call length() before getBuffer(minCapacity).
  *   If the length() was greater than minCapacity, then any contents after minCapacity
  *   may be lost.
  *   The buffer contents is not NUL-terminated by getBuffer().
  *   If length() < getCapacity() then you can terminate it by writing a NUL
  *   at index length().
  * - You must call releaseBuffer(newLength) before and in order to
  *   return to normal UnicodeString operation.
  *
  * @param minCapacity the minimum number of char16_ts that are to be available
  *        in the buffer, starting at the returned pointer;
  *        default to the current string capacity if minCapacity==-1
  * @return a writable pointer to the internal string buffer,
  *         or nullptr if an error occurs (nested calls, out of memory)
  *
  * @see releaseBuffer
  * @see getTerminatedBuffer()
  * @stable ICU 2.0
  */
 char16_t *getBuffer(int32_t minCapacity);

 /**
  * Release a read/write buffer on a UnicodeString object with an
  * "open" getBuffer(minCapacity).
  * This function must be called in a matched pair with getBuffer(minCapacity).
  * releaseBuffer(newLength) must be called if and only if a getBuffer(minCapacity) is "open".
  *
  * It will set the string length to newLength, at most to the current capacity.
  * If newLength==-1 then it will set the length according to the
  * first NUL in the buffer, or to the capacity if there is no NUL.
  *
  * After calling releaseBuffer(newLength) the UnicodeString is back to normal operation.
  *
  * @param newLength the new length of the UnicodeString object;
  *        defaults to the current capacity if newLength is greater than that;
  *        if newLength==-1, it defaults to u_strlen(buffer) but not more than
  *        the current capacity of the string
  *
  * @see getBuffer(int32_t minCapacity)
  * @stable ICU 2.0
  */
 void releaseBuffer(int32_t newLength=-1);

 /**
  * Get a read-only pointer to the internal buffer.
  * This can be called at any time on a valid UnicodeString.
  *
  * It returns 0 if the string is bogus, or
  * during an "open" getBuffer(minCapacity).
  *
  * It can be called as many times as desired.
  * The pointer that it returns will remain valid until the UnicodeString object is modified,
  * at which time the pointer is semantically invalidated and must not be used any more.
  *
  * The capacity of the buffer can be determined with getCapacity().
  * The part after length() may or may not be initialized and valid,
  * depending on the history of the UnicodeString object.
  *
  * The buffer contents is (probably) not NUL-terminated.
  * You can check if it is with
  * `(s.length() < s.getCapacity() && buffer[s.length()]==0)`.
  * (See getTerminatedBuffer().)
  *
  * The buffer may reside in read-only memory. Its contents must not
  * be modified.
  *
  * @return a read-only pointer to the internal string buffer,
  *         or nullptr if the string is empty or bogus
  *
  * @see getBuffer(int32_t minCapacity)
  * @see getTerminatedBuffer()
  * @stable ICU 2.0
  */
 inline const char16_t *getBuffer() const;

 /**
  * Get a read-only pointer to the internal buffer,
  * making sure that it is NUL-terminated.
  * This can be called at any time on a valid UnicodeString.
  *
  * It returns 0 if the string is bogus, or
  * during an "open" getBuffer(minCapacity), or if the buffer cannot
  * be NUL-terminated (because memory allocation failed).
  *
  * It can be called as many times as desired.
  * The pointer that it returns will remain valid until the UnicodeString object is modified,
  * at which time the pointer is semantically invalidated and must not be used any more.
  *
  * The capacity of the buffer can be determined with getCapacity().
  * The part after length()+1 may or may not be initialized and valid,
  * depending on the history of the UnicodeString object.
  *
  * The buffer contents is guaranteed to be NUL-terminated.
  * getTerminatedBuffer() may reallocate the buffer if a terminating NUL
  * is written.
  * For this reason, this function is not const, unlike getBuffer().
  * Note that a UnicodeString may also contain NUL characters as part of its contents.
  *
  * The buffer may reside in read-only memory. Its contents must not
  * be modified.
  *
  * @return a read-only pointer to the internal string buffer,
  *         or 0 if the string is empty or bogus
  *
  * @see getBuffer(int32_t minCapacity)
  * @see getBuffer()
  * @stable ICU 2.2
  */
 const char16_t *getTerminatedBuffer();

 /**
  * Converts to a std::u16string_view.
  *
  * @return a string view of the contents of this string
  * @stable ICU 76
  */
 inline operator std::u16string_view() const {
   return {getBuffer(), static_cast<std::u16string_view::size_type>(length())};
 }

#if U_SIZEOF_WCHAR_T==2 || defined(U_IN_DOXYGEN)
 /**
  * Converts to a std::wstring_view.
  *
  * Note: This should remain draft until C++ standard plans
  * about char16_t vs. wchar_t become clearer.
  *
  * @return a string view of the contents of this string
  * @stable ICU 76
  */
 inline operator std::wstring_view() const {
   const char16_t *p = getBuffer();
#ifdef U_ALIASING_BARRIER
   U_ALIASING_BARRIER(p);
#endif
   return { reinterpret_cast<const wchar_t *>(p), (std::wstring_view::size_type)length() };
 }
#endif  // U_SIZEOF_WCHAR_T

 //========================================
 // Constructors
 //========================================

 /** Construct an empty UnicodeString.
  * @stable ICU 2.0
  */
 inline UnicodeString();

 /**
  * Construct a UnicodeString with capacity to hold `capacity` char16_ts
  * @param capacity the number of char16_ts this UnicodeString should hold
  * before a resize is necessary; if count is greater than 0 and count
  * code points c take up more space than capacity, then capacity is adjusted
  * accordingly.
  * @param c is used to initially fill the string
  * @param count specifies how many code points c are to be written in the
  *              string
  * @stable ICU 2.0
  */
 UnicodeString(int32_t capacity, UChar32 c, int32_t count);

 /**
  * Single char16_t (code unit) constructor.
  *
  * It is recommended to mark this constructor "explicit" by
  * `-DUNISTR_FROM_CHAR_EXPLICIT=explicit`
  * on the compiler command line or similar.
  * @param ch the character to place in the UnicodeString
  * @stable ICU 2.0
  */
 UNISTR_FROM_CHAR_EXPLICIT UnicodeString(char16_t ch);

 /**
  * Single UChar32 (code point) constructor.
  *
  * It is recommended to mark this constructor "explicit" by
  * `-DUNISTR_FROM_CHAR_EXPLICIT=explicit`
  * on the compiler command line or similar.
  * @param ch the character to place in the UnicodeString
  * @stable ICU 2.0
  */
 UNISTR_FROM_CHAR_EXPLICIT UnicodeString(UChar32 ch);

#ifdef U_HIDE_DRAFT_API
 /**
  * char16_t* constructor.
  *
  * It is recommended to mark this constructor "explicit" by
  * `-DUNISTR_FROM_STRING_EXPLICIT=explicit`
  * on the compiler command line or similar.
  *
  * Note, for string literals:
  * Since C++17 and ICU 76, you can use UTF-16 string literals with compile-time
  * length determination:
  * \code
  * UnicodeString str(u"literal");
  * if (str == u"other literal") { ... }
  * \endcode
  *
  * @param text The characters to place in the UnicodeString.  `text`
  * must be NUL (U+0000) terminated.
  * @stable ICU 2.0
  */
 UNISTR_FROM_STRING_EXPLICIT UnicodeString(const char16_t *text) :
     UnicodeString(text, -1) {}
#endif  // U_HIDE_DRAFT_API

#if !U_CHAR16_IS_TYPEDEF && \
   (defined(U_HIDE_DRAFT_API) || (defined(_LIBCPP_VERSION) && _LIBCPP_VERSION >= 180000))
 /**
  * uint16_t * constructor.
  * Delegates to UnicodeString(const char16_t *).
  *
  * It is recommended to mark this constructor "explicit" by
  * `-DUNISTR_FROM_STRING_EXPLICIT=explicit`
  * on the compiler command line or similar.
  *
  * Note, for string literals:
  * Since C++17 and ICU 76, you can use UTF-16 string literals with compile-time
  * length determination:
  * \code
  * UnicodeString str(u"literal");
  * if (str == u"other literal") { ... }
  * \endcode
  *
  * @param text NUL-terminated UTF-16 string
  * @stable ICU 59
  */
 UNISTR_FROM_STRING_EXPLICIT UnicodeString(const uint16_t *text) :
     UnicodeString(ConstChar16Ptr(text), -1) {}
#endif

#if defined(U_HIDE_DRAFT_API) && (U_SIZEOF_WCHAR_T==2 || defined(U_IN_DOXYGEN))
 /**
  * wchar_t * constructor.
  * (Only defined if U_SIZEOF_WCHAR_T==2.)
  * Delegates to UnicodeString(const char16_t *).
  *
  * It is recommended to mark this constructor "explicit" by
  * `-DUNISTR_FROM_STRING_EXPLICIT=explicit`
  * on the compiler command line or similar.
  *
  * Note, for string literals:
  * Since C++17 and ICU 76, you can use UTF-16 string literals with compile-time
  * length determination:
  * \code
  * UnicodeString str(u"literal");
  * if (str == u"other literal") { ... }
  * \endcode
  *
  * @param text NUL-terminated UTF-16 string
  * @stable ICU 59
  */
 UNISTR_FROM_STRING_EXPLICIT UnicodeString(const wchar_t *text) :
     UnicodeString(ConstChar16Ptr(text), -1) {}
#endif

 /**
  * nullptr_t constructor.
  * Effectively the same as the default constructor, makes an empty string object.
  *
  * It is recommended to mark this constructor "explicit" by
  * `-DUNISTR_FROM_STRING_EXPLICIT=explicit`
  * on the compiler command line or similar.
  * @param text nullptr
  * @stable ICU 59
  */
 UNISTR_FROM_STRING_EXPLICIT inline UnicodeString(const std::nullptr_t text);

 /**
  * char16_t* constructor.
  *
  * Note, for string literals:
  * Since C++17 and ICU 76, you can use UTF-16 string literals with compile-time
  * length determination:
  * \code
  * UnicodeString str(u"literal");
  * if (str == u"other literal") { ... }
  * \endcode
  *
  * @param text The characters to place in the UnicodeString.
  * @param textLength The number of Unicode characters in `text`
  * to copy.
  * @stable ICU 2.0
  */
 UnicodeString(const char16_t *text,
       int32_t textLength);

#if !U_CHAR16_IS_TYPEDEF
 /**
  * uint16_t * constructor.
  * Delegates to UnicodeString(const char16_t *, int32_t).
  *
  * Note, for string literals:
  * Since C++17 and ICU 76, you can use UTF-16 string literals with compile-time
  * length determination:
  * \code
  * UnicodeString str(u"literal");
  * if (str == u"other literal") { ... }
  * \endcode
  *
  * @param text UTF-16 string
  * @param textLength string length
  * @stable ICU 59
  */
 UnicodeString(const uint16_t *text, int32_t textLength) :
     UnicodeString(ConstChar16Ptr(text), textLength) {}
#endif

#if U_SIZEOF_WCHAR_T==2 || defined(U_IN_DOXYGEN)
 /**
  * wchar_t * constructor.
  * (Only defined if U_SIZEOF_WCHAR_T==2.)
  * Delegates to UnicodeString(const char16_t *, int32_t).
  *
  * Note, for string literals:
  * Since C++17 and ICU 76, you can use UTF-16 string literals with compile-time
  * length determination:
  * \code
  * UnicodeString str(u"literal");
  * if (str == u"other literal") { ... }
  * \endcode
  *
  * @param text UTF-16 string
  * @param textLength string length
  * @stable ICU 59
  */
 UnicodeString(const wchar_t *text, int32_t textLength) :
     UnicodeString(ConstChar16Ptr(text), textLength) {}
#endif

 /**
  * nullptr_t constructor.
  * Effectively the same as the default constructor, makes an empty string object.
  * @param text nullptr
  * @param textLength ignored
  * @stable ICU 59
  */
 inline UnicodeString(const std::nullptr_t text, int32_t textLength);

 /**
  * Constructor from `text`
  * which is, or which is implicitly convertible to,
  * a std::u16string_view or (if U_SIZEOF_WCHAR_T==2) std::wstring_view.
  * The string is bogus if the string view is too long.
  *
  * If you need a UnicodeString but need not copy the string view contents,
  * then you can call the UnicodeString::readOnlyAlias() function instead of this constructor.
  *
  * @param text UTF-16 string
  * @stable ICU 76
  */
 template<typename S, typename = std::enable_if_t<ConvertibleToU16StringView<S>>>
 UNISTR_FROM_STRING_EXPLICIT UnicodeString(const S &text) {
   fUnion.fFields.fLengthAndFlags = kShortString;
   doAppend(internal::toU16StringViewNullable(text));
 }

 /**
  * Readonly-aliasing char16_t* constructor.
  * The text will be used for the UnicodeString object, but
  * it will not be released when the UnicodeString is destroyed.
  * This has copy-on-write semantics:
  * When the string is modified, then the buffer is first copied into
  * newly allocated memory.
  * The aliased buffer is never modified.
  *
  * In an assignment to another UnicodeString, when using the copy constructor
  * or the assignment operator, the text will be copied.
  * When using fastCopyFrom(), the text will be aliased again,
  * so that both strings then alias the same readonly-text.
  *
  * Note, for string literals:
  * Since C++17 and ICU 76, you can use UTF-16 string literals with compile-time
  * length determination:
  * \code
  * UnicodeString alias = UnicodeString::readOnlyAlias(u"literal");
  * if (str == u"other literal") { ... }
  * \endcode
  *
  * @param isTerminated specifies if `text` is `NUL`-terminated.
  *                     This must be true if `textLength==-1`.
  * @param text The characters to alias for the UnicodeString.
  * @param textLength The number of Unicode characters in `text` to alias.
  *                   If -1, then this constructor will determine the length
  *                   by calling `u_strlen()`.
  * @stable ICU 2.0
  */
 UnicodeString(UBool isTerminated,
               ConstChar16Ptr text,
               int32_t textLength);

 /**
  * Writable-aliasing char16_t* constructor.
  * The text will be used for the UnicodeString object, but
  * it will not be released when the UnicodeString is destroyed.
  * This has write-through semantics:
  * For as long as the capacity of the buffer is sufficient, write operations
  * will directly affect the buffer. When more capacity is necessary, then
  * a new buffer will be allocated and the contents copied as with regularly
  * constructed strings.
  * In an assignment to another UnicodeString, the buffer will be copied.
  * The extract(Char16Ptr dst) function detects whether the dst pointer is the same
  * as the string buffer itself and will in this case not copy the contents.
  *
  * @param buffer The characters to alias for the UnicodeString.
  * @param buffLength The number of Unicode characters in `buffer` to alias.
  * @param buffCapacity The size of `buffer` in char16_ts.
  * @stable ICU 2.0
  */
 UnicodeString(char16_t *buffer, int32_t buffLength, int32_t buffCapacity);

#if !U_CHAR16_IS_TYPEDEF
 /**
  * Writable-aliasing uint16_t * constructor.
  * Delegates to UnicodeString(const char16_t *, int32_t, int32_t).
  * @param buffer writable buffer of/for UTF-16 text
  * @param buffLength length of the current buffer contents
  * @param buffCapacity buffer capacity
  * @stable ICU 59
  */
 UnicodeString(uint16_t *buffer, int32_t buffLength, int32_t buffCapacity) :
     UnicodeString(Char16Ptr(buffer), buffLength, buffCapacity) {}
#endif

#if U_SIZEOF_WCHAR_T==2 || defined(U_IN_DOXYGEN)
 /**
  * Writable-aliasing wchar_t * constructor.
  * (Only defined if U_SIZEOF_WCHAR_T==2.)
  * Delegates to UnicodeString(const char16_t *, int32_t, int32_t).
  * @param buffer writable buffer of/for UTF-16 text
  * @param buffLength length of the current buffer contents
  * @param buffCapacity buffer capacity
  * @stable ICU 59
  */
 UnicodeString(wchar_t *buffer, int32_t buffLength, int32_t buffCapacity) :
     UnicodeString(Char16Ptr(buffer), buffLength, buffCapacity) {}
#endif

 /**
  * Writable-aliasing nullptr_t constructor.
  * Effectively the same as the default constructor, makes an empty string object.
  * @param buffer nullptr
  * @param buffLength ignored
  * @param buffCapacity ignored
  * @stable ICU 59
  */
 inline UnicodeString(std::nullptr_t buffer, int32_t buffLength, int32_t buffCapacity);

#if U_CHARSET_IS_UTF8 || !UCONFIG_NO_CONVERSION

 /**
  * char* constructor.
  * Uses the default converter (and thus depends on the ICU conversion code)
  * unless U_CHARSET_IS_UTF8 is set to 1.
  *
  * For ASCII (really "invariant character") strings it is more efficient to use
  * the constructor that takes a US_INV (for its enum EInvariant).
  *
  * Note, for string literals:
  * Since C++17 and ICU 76, you can use UTF-16 string literals with compile-time
  * length determination:
  * \code
  * UnicodeString str(u"literal");
  * if (str == u"other literal") { ... }
  * \endcode
  *
  * It is recommended to mark this constructor "explicit" by
  * `-DUNISTR_FROM_STRING_EXPLICIT=explicit`
  * on the compiler command line or similar.
  * @param codepageData an array of bytes, null-terminated,
  *                     in the platform's default codepage.
  * @stable ICU 2.0
  */
 UNISTR_FROM_STRING_EXPLICIT UnicodeString(const char *codepageData);

 /**
  * char* constructor.
  * Uses the default converter (and thus depends on the ICU conversion code)
  * unless U_CHARSET_IS_UTF8 is set to 1.
  * @param codepageData an array of bytes in the platform's default codepage.
  * @param dataLength The number of bytes in `codepageData`.
  * @stable ICU 2.0
  */
 UnicodeString(const char *codepageData, int32_t dataLength);

#endif

#if !UCONFIG_NO_CONVERSION

 /**
  * char* constructor.
  * @param codepageData an array of bytes, null-terminated
  * @param codepage the encoding of `codepageData`.  The special
  * value 0 for `codepage` indicates that the text is in the
  * platform's default codepage.
  *
  * If `codepage` is an empty string (`""`),
  * then a simple conversion is performed on the codepage-invariant
  * subset ("invariant characters") of the platform encoding. See utypes.h.
  * Recommendation: For invariant-character strings use the constructor
  * UnicodeString(const char *src, int32_t length, enum EInvariant inv)
  * because it avoids object code dependencies of UnicodeString on
  * the conversion code.
  *
  * @stable ICU 2.0
  */
 UnicodeString(const char *codepageData, const char *codepage);

 /**
  * char* constructor.
  * @param codepageData an array of bytes.
  * @param dataLength The number of bytes in `codepageData`.
  * @param codepage the encoding of `codepageData`.  The special
  * value 0 for `codepage` indicates that the text is in the
  * platform's default codepage.
  * If `codepage` is an empty string (`""`),
  * then a simple conversion is performed on the codepage-invariant
  * subset ("invariant characters") of the platform encoding. See utypes.h.
  * Recommendation: For invariant-character strings use the constructor
  * UnicodeString(const char *src, int32_t length, enum EInvariant inv)
  * because it avoids object code dependencies of UnicodeString on
  * the conversion code.
  *
  * @stable ICU 2.0
  */
 UnicodeString(const char *codepageData, int32_t dataLength, const char *codepage);

 /**
  * char * / UConverter constructor.
  * This constructor uses an existing UConverter object to
  * convert the codepage string to Unicode and construct a UnicodeString
  * from that.
  *
  * The converter is reset at first.
  * If the error code indicates a failure before this constructor is called,
  * or if an error occurs during conversion or construction,
  * then the string will be bogus.
  *
  * This function avoids the overhead of opening and closing a converter if
  * multiple strings are constructed.
  *
  * @param src input codepage string
  * @param srcLength length of the input string, can be -1 for NUL-terminated strings
  * @param cnv converter object (ucnv_resetToUnicode() will be called),
  *        can be nullptr for the default converter
  * @param errorCode normal ICU error code
  * @stable ICU 2.0
  */
 UnicodeString(
       const char *src, int32_t srcLength,
       UConverter *cnv,
       UErrorCode &errorCode);

#endif

 /**
  * Constructs a Unicode string from an invariant-character char * string.
  * About invariant characters see utypes.h.
  * This constructor has no runtime dependency on conversion code and is
  * therefore recommended over ones taking a charset name string
  * (where the empty string "" indicates invariant-character conversion).
  *
  * Use the macro US_INV as the third, signature-distinguishing parameter.
  *
  * For example:
  * \code
  *     void fn(const char *s) {
  *       UnicodeString ustr(s, -1, US_INV);
  *       // use ustr ...
  *     }
  * \endcode
  *
  * Note, for string literals:
  * Since C++17 and ICU 76, you can use UTF-16 string literals with compile-time
  * length determination:
  * \code
  * UnicodeString str(u"literal");
  * if (str == u"other literal") { ... }
  * \endcode
  *
  * @param src String using only invariant characters.
  * @param textLength Length of src, or -1 if NUL-terminated.
  * @param inv Signature-distinguishing parameter, use US_INV.
  *
  * @see US_INV
  * @stable ICU 3.2
  */
 UnicodeString(const char *src, int32_t textLength, enum EInvariant inv);


 /**
  * Copy constructor.
  *
  * Starting with ICU 2.4, the assignment operator and the copy constructor
  * allocate a new buffer and copy the buffer contents even for readonly aliases.
  * By contrast, the fastCopyFrom() function implements the old,
  * more efficient but less safe behavior
  * of making this string also a readonly alias to the same buffer.
  *
  * If the source object has an "open" buffer from getBuffer(minCapacity),
  * then the copy is an empty string.
  *
  * @param that The UnicodeString object to copy.
  * @stable ICU 2.0
  * @see fastCopyFrom
  */
 UnicodeString(const UnicodeString& that);

 /**
  * Move constructor; might leave src in bogus state.
  * This string will have the same contents and state that the source string had.
  * @param src source string
  * @stable ICU 56
  */
 UnicodeString(UnicodeString &&src) noexcept;

 /**
  * 'Substring' constructor from tail of source string.
  * @param src The UnicodeString object to copy.
  * @param srcStart The offset into `src` at which to start copying.
  * @stable ICU 2.2
  */
 UnicodeString(const UnicodeString& src, int32_t srcStart);

 /**
  * 'Substring' constructor from subrange of source string.
  * @param src The UnicodeString object to copy.
  * @param srcStart The offset into `src` at which to start copying.
  * @param srcLength The number of characters from `src` to copy.
  * @stable ICU 2.2
  */
 UnicodeString(const UnicodeString& src, int32_t srcStart, int32_t srcLength);

 /**
  * Clone this object, an instance of a subclass of Replaceable.
  * Clones can be used concurrently in multiple threads.
  * If a subclass does not implement clone(), or if an error occurs,
  * then nullptr is returned.
  * The caller must delete the clone.
  *
  * @return a clone of this object
  *
  * @see Replaceable::clone
  * @see getDynamicClassID
  * @stable ICU 2.6
  */
 virtual UnicodeString *clone() const override;

 /** Destructor.
  * @stable ICU 2.0
  */
 virtual ~UnicodeString();

 /**
  * Readonly-aliasing factory method.
  * Aliases the same buffer as the input `text`
  * which is, or which is implicitly convertible to,
  * a std::u16string_view or (if U_SIZEOF_WCHAR_T==2) std::wstring_view.
  * The string is bogus if the string view is too long.
  *
  * The text will be used for the UnicodeString object, but
  * it will not be released when the UnicodeString is destroyed.
  * This has copy-on-write semantics:
  * When the string is modified, then the buffer is first copied into
  * newly allocated memory.
  * The aliased buffer is never modified.
  *
  * In an assignment to another UnicodeString, when using the copy constructor
  * or the assignment operator, the text will be copied.
  * When using fastCopyFrom(), the text will be aliased again,
  * so that both strings then alias the same readonly-text.
  *
  * @param text The string view to alias for the UnicodeString.
  * @stable ICU 76
  */
 template<typename S, typename = std::enable_if_t<ConvertibleToU16StringView<S>>>
 static inline UnicodeString readOnlyAlias(const S &text) {
   return readOnlyAliasFromU16StringView(internal::toU16StringView(text));
 }

 /**
  * Readonly-aliasing factory method.
  * Aliases the same buffer as the input `text`.
  *
  * The text will be used for the UnicodeString object, but
  * it will not be released when the UnicodeString is destroyed.
  * This has copy-on-write semantics:
  * When the string is modified, then the buffer is first copied into
  * newly allocated memory.
  * The aliased buffer is never modified.
  *
  * In an assignment to another UnicodeString, when using the copy constructor
  * or the assignment operator, the text will be copied.
  * When using fastCopyFrom(), the text will be aliased again,
  * so that both strings then alias the same readonly-text.
  *
  * @param text The UnicodeString to alias.
  * @stable ICU 76
  */
 static inline UnicodeString readOnlyAlias(const UnicodeString &text) {
   return readOnlyAliasFromUnicodeString(text);
 }

 /**
  * Create a UnicodeString from a UTF-8 string.
  * Illegal input is replaced with U+FFFD. Otherwise, errors result in a bogus string.
  * Calls u_strFromUTF8WithSub().
  *
  * @param utf8 UTF-8 input string.
  *             Note that a StringPiece can be implicitly constructed
  *             from a std::string or a NUL-terminated const char * string.
  * @return A UnicodeString with equivalent UTF-16 contents.
  * @see toUTF8
  * @see toUTF8String
  * @stable ICU 4.2
  */
 static UnicodeString fromUTF8(StringPiece utf8);

 /**
  * Create a UnicodeString from a UTF-32 string.
  * Illegal input is replaced with U+FFFD. Otherwise, errors result in a bogus string.
  * Calls u_strFromUTF32WithSub().
  *
  * @param utf32 UTF-32 input string. Must not be nullptr.
  * @param length Length of the input string, or -1 if NUL-terminated.
  * @return A UnicodeString with equivalent UTF-16 contents.
  * @see toUTF32
  * @stable ICU 4.2
  */
 static UnicodeString fromUTF32(const UChar32 *utf32, int32_t length);

 /* Miscellaneous operations */

 /**
  * Unescape a string of characters and return a string containing
  * the result.  The following escape sequences are recognized:
  *
  * \\uhhhh       4 hex digits; h in [0-9A-Fa-f]
  * \\Uhhhhhhhh   8 hex digits
  * \\xhh         1-2 hex digits
  * \\ooo         1-3 octal digits; o in [0-7]
  * \\cX          control-X; X is masked with 0x1F
  *
  * as well as the standard ANSI C escapes:
  *
  * \\a => U+0007, \\b => U+0008, \\t => U+0009, \\n => U+000A,
  * \\v => U+000B, \\f => U+000C, \\r => U+000D, \\e => U+001B,
  * \\" => U+0022, \\' => U+0027, \\? => U+003F, \\\\ => U+005C
  *
  * Anything else following a backslash is generically escaped.  For
  * example, "[a\\-z]" returns "[a-z]".
  *
  * If an escape sequence is ill-formed, this method returns an empty
  * string.  An example of an ill-formed sequence is "\\u" followed by
  * fewer than 4 hex digits.
  *
  * This function is similar to u_unescape() but not identical to it.
  * The latter takes a source char*, so it does escape recognition
  * and also invariant conversion.
  *
  * @return a string with backslash escapes interpreted, or an
  * empty string on error.
  * @see UnicodeString#unescapeAt()
  * @see u_unescape()
  * @see u_unescapeAt()
  * @stable ICU 2.0
  */
 UnicodeString unescape() const;

 /**
  * Unescape a single escape sequence and return the represented
  * character.  See unescape() for a listing of the recognized escape
  * sequences.  The character at offset-1 is assumed (without
  * checking) to be a backslash.  If the escape sequence is
  * ill-formed, or the offset is out of range, U_SENTINEL=-1 is
  * returned.
  *
  * @param offset an input output parameter.  On input, it is the
  * offset into this string where the escape sequence is located,
  * after the initial backslash.  On output, it is advanced after the
  * last character parsed.  On error, it is not advanced at all.
  * @return the character represented by the escape sequence at
  * offset, or U_SENTINEL=-1 on error.
  * @see UnicodeString#unescape()
  * @see u_unescape()
  * @see u_unescapeAt()
  * @stable ICU 2.0
  */
 UChar32 unescapeAt(int32_t &offset) const;

 /**
  * ICU "poor man's RTTI", returns a UClassID for this class.
  *
  * @stable ICU 2.2
  */
 static UClassID U_EXPORT2 getStaticClassID();

 /**
  * ICU "poor man's RTTI", returns a UClassID for the actual class.
  *
  * @stable ICU 2.2
  */
 virtual UClassID getDynamicClassID() const override;

 //========================================
 // Implementation methods
 //========================================

protected:
 /**
  * Implement Replaceable::getLength() (see jitterbug 1027).
  * @stable ICU 2.4
  */
 virtual int32_t getLength() const override;

 /**
  * The change in Replaceable to use virtual getCharAt() allows
  * UnicodeString::charAt() to be inline again (see jitterbug 709).
  * @stable ICU 2.4
  */
 virtual char16_t getCharAt(int32_t offset) const override;

 /**
  * The change in Replaceable to use virtual getChar32At() allows
  * UnicodeString::char32At() to be inline again (see jitterbug 709).
  * @stable ICU 2.4
  */
 virtual UChar32 getChar32At(int32_t offset) const override;

private:
 static UnicodeString readOnlyAliasFromU16StringView(std::u16string_view text);
 static UnicodeString readOnlyAliasFromUnicodeString(const UnicodeString &text);

 // For char* constructors. Could be made public.
 UnicodeString &setToUTF8(StringPiece utf8);
 // For extract(char*).
 // We could make a toUTF8(target, capacity, errorCode) public but not
 // this version: New API will be cleaner if we make callers create substrings
 // rather than having start+length on every method,
 // and it should take a UErrorCode&.
 int32_t
 toUTF8(int32_t start, int32_t len,
        char *target, int32_t capacity) const;

 /**
  * Internal string contents comparison, called by operator==.
  * Requires: this & text not bogus and have same lengths.
  */
 inline UBool doEquals(const UnicodeString &text, int32_t len) const {
   return doEquals(text.getArrayStart(), len);
 }
 UBool doEquals(const char16_t *text, int32_t len) const;

 inline UBool
 doEqualsSubstring(int32_t start,
          int32_t length,
          const UnicodeString& srcText,
          int32_t srcStart,
          int32_t srcLength) const;

 UBool doEqualsSubstring(int32_t start,
          int32_t length,
          const char16_t *srcChars,
          int32_t srcStart,
          int32_t srcLength) const;

 inline int8_t
 doCompare(int32_t start,
          int32_t length,
          const UnicodeString& srcText,
          int32_t srcStart,
          int32_t srcLength) const;

 int8_t doCompare(int32_t start,
          int32_t length,
          const char16_t *srcChars,
          int32_t srcStart,
          int32_t srcLength) const;

 inline int8_t
 doCompareCodePointOrder(int32_t start,
                         int32_t length,
                         const UnicodeString& srcText,
                         int32_t srcStart,
                         int32_t srcLength) const;

 int8_t doCompareCodePointOrder(int32_t start,
                                int32_t length,
                                const char16_t *srcChars,
                                int32_t srcStart,
                                int32_t srcLength) const;

 inline int8_t
 doCaseCompare(int32_t start,
               int32_t length,
               const UnicodeString &srcText,
               int32_t srcStart,
               int32_t srcLength,
               uint32_t options) const;

 int8_t
 doCaseCompare(int32_t start,
               int32_t length,
               const char16_t *srcChars,
               int32_t srcStart,
               int32_t srcLength,
               uint32_t options) const;

 int32_t doIndexOf(char16_t c,
           int32_t start,
           int32_t length) const;

 int32_t doIndexOf(UChar32 c,
                       int32_t start,
                       int32_t length) const;

 int32_t doLastIndexOf(char16_t c,
               int32_t start,
               int32_t length) const;

 int32_t doLastIndexOf(UChar32 c,
                           int32_t start,
                           int32_t length) const;

 void doExtract(int32_t start,
        int32_t length,
        char16_t *dst,
        int32_t dstStart) const;

 inline void doExtract(int32_t start,
        int32_t length,
        UnicodeString& target) const;

 inline char16_t doCharAt(int32_t offset)  const;

 UnicodeString& doReplace(int32_t start,
              int32_t length,
              const UnicodeString& srcText,
              int32_t srcStart,
              int32_t srcLength);

 UnicodeString& doReplace(int32_t start,
              int32_t length,
              const char16_t *srcChars,
              int32_t srcStart,
              int32_t srcLength);
 UnicodeString& doReplace(int32_t start, int32_t length, std::u16string_view src);

 UnicodeString& doAppend(const UnicodeString& src, int32_t srcStart, int32_t srcLength);
 UnicodeString& doAppend(const char16_t *srcChars, int32_t srcStart, int32_t srcLength);
 UnicodeString& doAppend(std::u16string_view src);

 UnicodeString& doReverse(int32_t start,
              int32_t length);

 // calculate hash code
 int32_t doHashCode() const;

 // get pointer to start of array
 // these do not check for kOpenGetBuffer, unlike the public getBuffer() function
 inline char16_t* getArrayStart();
 inline const char16_t* getArrayStart() const;

 inline UBool hasShortLength() const;
 inline int32_t getShortLength() const;

 // A UnicodeString object (not necessarily its current buffer)
 // is writable unless it isBogus() or it has an "open" getBuffer(minCapacity).
 inline UBool isWritable() const;

 // Is the current buffer writable?
 inline UBool isBufferWritable() const;

 // None of the following does releaseArray().
 inline void setZeroLength();
 inline void setShortLength(int32_t len);
 inline void setLength(int32_t len);
 inline void setToEmpty();
 inline void setArray(char16_t *array, int32_t len, int32_t capacity); // sets length but not flags

 // allocate the array; result may be the stack buffer
 // sets refCount to 1 if appropriate
 // sets fArray, fCapacity, and flags
 // sets length to 0
 // returns boolean for success or failure
 UBool allocate(int32_t capacity);

 // release the array if owned
 void releaseArray();

 // turn a bogus string into an empty one
 void unBogus();

 // implements assignment operator, copy constructor, and fastCopyFrom()
 UnicodeString &copyFrom(const UnicodeString &src, UBool fastCopy=false);

 // Copies just the fields without memory management.
 void copyFieldsFrom(UnicodeString &src, UBool setSrcToBogus) noexcept;

 // Pin start and limit to acceptable values.
 inline void pinIndex(int32_t& start) const;
 inline void pinIndices(int32_t& start,
                        int32_t& length) const;

#if !UCONFIG_NO_CONVERSION

 /* Internal extract() using UConverter. */
 int32_t doExtract(int32_t start, int32_t length,
                   char *dest, int32_t destCapacity,
                   UConverter *cnv,
                   UErrorCode &errorCode) const;

 /*
  * Real constructor for converting from codepage data.
  * It assumes that it is called with !fRefCounted.
  *
  * If `codepage==0`, then the default converter
  * is used for the platform encoding.
  * If `codepage` is an empty string (`""`),
  * then a simple conversion is performed on the codepage-invariant
  * subset ("invariant characters") of the platform encoding. See utypes.h.
  */
 void doCodepageCreate(const char *codepageData,
                       int32_t dataLength,
                       const char *codepage);

 /*
  * Worker function for creating a UnicodeString from
  * a codepage string using a UConverter.
  */
 void
 doCodepageCreate(const char *codepageData,
                  int32_t dataLength,
                  UConverter *converter,
                  UErrorCode &status);

#endif

 /*
  * This function is called when write access to the array
  * is necessary.
  *
  * We need to make a copy of the array if
  * the buffer is read-only, or
  * the buffer is refCounted (shared), and refCount>1, or
  * the buffer is too small.
  *
  * Return false if memory could not be allocated.
  */
 UBool cloneArrayIfNeeded(int32_t newCapacity = -1,
                          int32_t growCapacity = -1,
                          UBool doCopyArray = true,
                          int32_t** pBufferToDelete = nullptr,
                          UBool forceClone = false);

 /**
  * Common function for UnicodeString case mappings.
  * The stringCaseMapper has the same type UStringCaseMapper
  * as in ustr_imp.h for ustrcase_map().
  */
 UnicodeString &
 caseMap(int32_t caseLocale, uint32_t options,
#if !UCONFIG_NO_BREAK_ITERATION
         BreakIterator *iter,
#endif
         UStringCaseMapper *stringCaseMapper);

 // ref counting
 void addRef();
 int32_t removeRef();
 int32_t refCount() const;

 // constants
 enum {
   /**
    * Size of stack buffer for short strings.
    * Must be at least U16_MAX_LENGTH for the single-code point constructor to work.
    * @see UNISTR_OBJECT_SIZE
    */
   US_STACKBUF_SIZE = static_cast<int32_t>(UNISTR_OBJECT_SIZE - sizeof(void*) - 2) / U_SIZEOF_UCHAR,
   kInvalidUChar=0xffff, // U+FFFF returned by charAt(invalid index)
   kInvalidHashCode=0, // invalid hash code
   kEmptyHashCode=1, // hash code for empty string

   // bit flag values for fLengthAndFlags
   kIsBogus=1,         // this string is bogus, i.e., not valid or nullptr
   kUsingStackBuffer=2,// using fUnion.fStackFields instead of fUnion.fFields
   kRefCounted=4,      // there is a refCount field before the characters in fArray
   kBufferIsReadonly=8,// do not write to this buffer
   kOpenGetBuffer=16,  // getBuffer(minCapacity) was called (is "open"),
                       // and releaseBuffer(newLength) must be called
   kAllStorageFlags=0x1f,

   kLengthShift=5,     // remaining 11 bits for non-negative short length, or negative if long
   kLength1=1<<kLengthShift,
   kMaxShortLength=0x3ff,  // max non-negative short length (leaves top bit 0)
   kLengthIsLarge=0xffe0,  // short length < 0, real length is in fUnion.fFields.fLength

   // combined values for convenience
   kShortString=kUsingStackBuffer,
   kLongString=kRefCounted,
   kReadonlyAlias=kBufferIsReadonly,
   kWritableAlias=0
 };

 friend class UnicodeStringAppendable;

 union StackBufferOrFields;        // forward declaration necessary before friend declaration
 friend union StackBufferOrFields; // make US_STACKBUF_SIZE visible inside fUnion

 /*
  * The following are all the class fields that are stored
  * in each UnicodeString object.
  * Note that UnicodeString has virtual functions,
  * therefore there is an implicit vtable pointer
  * as the first real field.
  * The fields should be aligned such that no padding is necessary.
  * On 32-bit machines, the size should be 32 bytes,
  * on 64-bit machines (8-byte pointers), it should be 40 bytes.
  *
  * We use a hack to achieve this.
  *
  * With at least some compilers, each of the following is forced to
  * a multiple of sizeof(pointer) [the largest field base unit here is a data pointer],
  * rounded up with additional padding if the fields do not already fit that requirement:
  * - sizeof(class UnicodeString)
  * - offsetof(UnicodeString, fUnion)
  * - sizeof(fUnion)
  * - sizeof(fStackFields)
  *
  * We optimize for the longest possible internal buffer for short strings.
  * fUnion.fStackFields begins with 2 bytes for storage flags
  * and the length of relatively short strings,
  * followed by the buffer for short string contents.
  * There is no padding inside fStackFields.
  *
  * Heap-allocated and aliased strings use fUnion.fFields.
  * Both fStackFields and fFields must begin with the same fields for flags and short length,
  * that is, those must have the same memory offsets inside the object,
  * because the flags must be inspected in order to decide which half of fUnion is being used.
  * We assume that the compiler does not reorder the fields.
  *
  * (Padding at the end of fFields is ok:
  * As long as it is no larger than fStackFields, it is not wasted space.)
  *
  * For some of the history of the UnicodeString class fields layout, see
  * - ICU ticket #11551 "longer UnicodeString contents in stack buffer"
  * - ICU ticket #11336 "UnicodeString: recombine stack buffer arrays"
  * - ICU ticket #8322 "why is sizeof(UnicodeString)==48?"
  */
 // (implicit) *vtable;
 union StackBufferOrFields {
   // fStackFields is used iff (fLengthAndFlags&kUsingStackBuffer) else fFields is used.
   // Each struct of the union must begin with fLengthAndFlags.
   struct {
     int16_t fLengthAndFlags;          // bit fields: see constants above
     char16_t fBuffer[US_STACKBUF_SIZE];  // buffer for short strings
   } fStackFields;
   struct {
     int16_t fLengthAndFlags;          // bit fields: see constants above
     int32_t fLength;    // number of characters in fArray if >127; else undefined
     int32_t fCapacity;  // capacity of fArray (in char16_ts)
     // array pointer last to minimize padding for machines with P128 data model
     // or pointer sizes that are not a power of 2
     char16_t   *fArray;    // the Unicode data
   } fFields;
 } fUnion;
};

/**
* Creates a new UnicodeString from the concatenation of two others.
*
* @param s1 The first string to be copied to the new one.
* @param s2 The second string to be copied to the new one, after s1.
* @return UnicodeString(s1).append(s2)
* @stable ICU 2.8
*/
U_COMMON_API UnicodeString U_EXPORT2
operator+ (const UnicodeString &s1, const UnicodeString &s2);

/**
* Creates a new UnicodeString from the concatenation of a UnicodeString and `s2`
* which is, or which is implicitly convertible to,
* a std::u16string_view or (if U_SIZEOF_WCHAR_T==2) std::wstring_view.
*
* @param s1 The string to be copied to the new one.
* @param s2 The string view to be copied to the new string, after s1.
* @return UnicodeString(s1).append(s2)
* @stable ICU 76
*/
template<typename S, typename = std::enable_if_t<ConvertibleToU16StringView<S>>>
inline UnicodeString operator+(const UnicodeString &s1, const S &s2) {
 return unistr_internalConcat(s1, internal::toU16StringView(s2));
}

#ifndef U_FORCE_HIDE_INTERNAL_API
/** @internal */
U_COMMON_API UnicodeString U_EXPORT2
unistr_internalConcat(const UnicodeString &s1, std::u16string_view s2);
#endif

//========================================
// Inline members
//========================================

//========================================
// Privates
//========================================

inline void
UnicodeString::pinIndex(int32_t& start) const
{
 // pin index
 if(start < 0) {
   start = 0;
 } else if(start > length()) {
   start = length();
 }
}

inline void
UnicodeString::pinIndices(int32_t& start,
                         int32_t& _length) const
{
 // pin indices
 int32_t len = length();
 if(start < 0) {
   start = 0;
 } else if(start > len) {
   start = len;
 }
 if(_length < 0) {
   _length = 0;
 } else if(_length > (len - start)) {
   _length = (len - start);
 }
}

inline char16_t*
UnicodeString::getArrayStart() {
 return (fUnion.fFields.fLengthAndFlags&kUsingStackBuffer) ?
   fUnion.fStackFields.fBuffer : fUnion.fFields.fArray;
}

inline const char16_t*
UnicodeString::getArrayStart() const {
 return (fUnion.fFields.fLengthAndFlags&kUsingStackBuffer) ?
   fUnion.fStackFields.fBuffer : fUnion.fFields.fArray;
}

//========================================
// Default constructor
//========================================

inline
UnicodeString::UnicodeString() {
 fUnion.fStackFields.fLengthAndFlags=kShortString;
}

inline UnicodeString::UnicodeString(const std::nullptr_t /*text*/) {
 fUnion.fStackFields.fLengthAndFlags=kShortString;
}

inline UnicodeString::UnicodeString(const std::nullptr_t /*text*/, int32_t /*length*/) {
 fUnion.fStackFields.fLengthAndFlags=kShortString;
}

inline UnicodeString::UnicodeString(std::nullptr_t /*buffer*/, int32_t /*buffLength*/, int32_t /*buffCapacity*/) {
 fUnion.fStackFields.fLengthAndFlags=kShortString;
}

//========================================
// Read-only implementation methods
//========================================
inline UBool
UnicodeString::hasShortLength() const {
 return fUnion.fFields.fLengthAndFlags>=0;
}

inline int32_t
UnicodeString::getShortLength() const {
 // fLengthAndFlags must be non-negative -> short length >= 0
 // and arithmetic or logical shift does not matter.
 return fUnion.fFields.fLengthAndFlags>>kLengthShift;
}

inline int32_t
UnicodeString::length() const {
 return hasShortLength() ? getShortLength() : fUnion.fFields.fLength;
}

inline int32_t
UnicodeString::getCapacity() const {
 return (fUnion.fFields.fLengthAndFlags&kUsingStackBuffer) ?
   US_STACKBUF_SIZE : fUnion.fFields.fCapacity;
}

inline int32_t
UnicodeString::hashCode() const
{ return doHashCode(); }

inline UBool
UnicodeString::isBogus() const
{ return fUnion.fFields.fLengthAndFlags & kIsBogus; }

inline UBool
UnicodeString::isWritable() const
{ return !(fUnion.fFields.fLengthAndFlags & (kOpenGetBuffer | kIsBogus)); }

inline UBool
UnicodeString::isBufferWritable() const
{
 return
     !(fUnion.fFields.fLengthAndFlags&(kOpenGetBuffer|kIsBogus|kBufferIsReadonly)) &&
     (!(fUnion.fFields.fLengthAndFlags&kRefCounted) || refCount()==1);
}

inline const char16_t *
UnicodeString::getBuffer() const {
 if(fUnion.fFields.fLengthAndFlags&(kIsBogus|kOpenGetBuffer)) {
   return nullptr;
 } else if(fUnion.fFields.fLengthAndFlags&kUsingStackBuffer) {
   return fUnion.fStackFields.fBuffer;
 } else {
   return fUnion.fFields.fArray;
 }
}

//========================================
// Read-only alias methods
//========================================
inline int8_t
UnicodeString::doCompare(int32_t start,
             int32_t thisLength,
             const UnicodeString& srcText,
             int32_t srcStart,
             int32_t srcLength) const
{
 if(srcText.isBogus()) {
   return static_cast<int8_t>(!isBogus()); // 0 if both are bogus, 1 otherwise
 } else {
   srcText.pinIndices(srcStart, srcLength);
   return doCompare(start, thisLength, srcText.getArrayStart(), srcStart, srcLength);
 }
}

inline UBool
UnicodeString::doEqualsSubstring(int32_t start,
             int32_t thisLength,
             const UnicodeString& srcText,
             int32_t srcStart,
             int32_t srcLength) const
{
 if(srcText.isBogus()) {
   return isBogus();
 } else {
   srcText.pinIndices(srcStart, srcLength);
   return !isBogus() && doEqualsSubstring(start, thisLength, srcText.getArrayStart(), srcStart, srcLength);
 }
}

inline bool
UnicodeString::operator== (const UnicodeString& text) const
{
 if(isBogus()) {
   return text.isBogus();
 } else {
   int32_t len = length(), textLength = text.length();
   return !text.isBogus() && len == textLength && doEquals(text, len);
 }
}

inline bool
UnicodeString::operator!= (const UnicodeString& text) const
{ return (! operator==(text)); }

inline UBool
UnicodeString::operator> (const UnicodeString& text) const
{ return doCompare(0, length(), text, 0, text.length()) == 1; }

inline UBool
UnicodeString::operator< (const UnicodeString& text) const
{ return doCompare(0, length(), text, 0, text.length()) == -1; }

inline UBool
UnicodeString::operator>= (const UnicodeString& text) const
{ return doCompare(0, length(), text, 0, text.length()) != -1; }

inline UBool
UnicodeString::operator<= (const UnicodeString& text) const
{ return doCompare(0, length(), text, 0, text.length()) != 1; }

inline int8_t
UnicodeString::compare(const UnicodeString& text) const
{ return doCompare(0, length(), text, 0, text.length()); }

inline int8_t
UnicodeString::compare(int32_t start,
              int32_t _length,
              const UnicodeString& srcText) const
{ return doCompare(start, _length, srcText, 0, srcText.length()); }

inline int8_t
UnicodeString::compare(ConstChar16Ptr srcChars,
              int32_t srcLength) const
{ return doCompare(0, length(), srcChars, 0, srcLength); }

inline int8_t
UnicodeString::compare(int32_t start,
              int32_t _length,
              const UnicodeString& srcText,
              int32_t srcStart,
              int32_t srcLength) const
{ return doCompare(start, _length, srcText, srcStart, srcLength); }

inline int8_t
UnicodeString::compare(int32_t start,
              int32_t _length,
              const char16_t *srcChars) const
{ return doCompare(start, _length, srcChars, 0, _length); }

inline int8_t
UnicodeString::compare(int32_t start,
              int32_t _length,
              const char16_t *srcChars,
              int32_t srcStart,
              int32_t srcLength) const
{ return doCompare(start, _length, srcChars, srcStart, srcLength); }

inline int8_t
UnicodeString::compareBetween(int32_t start,
                 int32_t limit,
                 const UnicodeString& srcText,
                 int32_t srcStart,
                 int32_t srcLimit) const
{ return doCompare(start, limit - start,
          srcText, srcStart, srcLimit - srcStart); }

inline int8_t
UnicodeString::doCompareCodePointOrder(int32_t start,
                                      int32_t thisLength,
                                      const UnicodeString& srcText,
                                      int32_t srcStart,
                                      int32_t srcLength) const
{
 if(srcText.isBogus()) {
   return static_cast<int8_t>(!isBogus()); // 0 if both are bogus, 1 otherwise
 } else {
   srcText.pinIndices(srcStart, srcLength);
   return doCompareCodePointOrder(start, thisLength, srcText.getArrayStart(), srcStart, srcLength);
 }
}

inline int8_t
UnicodeString::compareCodePointOrder(const UnicodeString& text) const
{ return doCompareCodePointOrder(0, length(), text, 0, text.length()); }

inline int8_t
UnicodeString::compareCodePointOrder(int32_t start,
                                    int32_t _length,
                                    const UnicodeString& srcText) const
{ return doCompareCodePointOrder(start, _length, srcText, 0, srcText.length()); }

inline int8_t
UnicodeString::compareCodePointOrder(ConstChar16Ptr srcChars,
                                    int32_t srcLength) const
{ return doCompareCodePointOrder(0, length(), srcChars, 0, srcLength); }

inline int8_t
UnicodeString::compareCodePointOrder(int32_t start,
                                    int32_t _length,
                                    const UnicodeString& srcText,
                                    int32_t srcStart,
                                    int32_t srcLength) const
{ return doCompareCodePointOrder(start, _length, srcText, srcStart, srcLength); }

inline int8_t
UnicodeString::compareCodePointOrder(int32_t start,
                                    int32_t _length,
                                    const char16_t *srcChars) const
{ return doCompareCodePointOrder(start, _length, srcChars, 0, _length); }

inline int8_t
UnicodeString::compareCodePointOrder(int32_t start,
                                    int32_t _length,
                                    const char16_t *srcChars,
                                    int32_t srcStart,
                                    int32_t srcLength) const
{ return doCompareCodePointOrder(start, _length, srcChars, srcStart, srcLength); }

inline int8_t
UnicodeString::compareCodePointOrderBetween(int32_t start,
                                           int32_t limit,
                                           const UnicodeString& srcText,
                                           int32_t srcStart,
                                           int32_t srcLimit) const
{ return doCompareCodePointOrder(start, limit - start,
          srcText, srcStart, srcLimit - srcStart); }

inline int8_t
UnicodeString::doCaseCompare(int32_t start,
                            int32_t thisLength,
                            const UnicodeString &srcText,
                            int32_t srcStart,
                            int32_t srcLength,
                            uint32_t options) const
{
 if(srcText.isBogus()) {
   return static_cast<int8_t>(!isBogus()); // 0 if both are bogus, 1 otherwise
 } else {
   srcText.pinIndices(srcStart, srcLength);
   return doCaseCompare(start, thisLength, srcText.getArrayStart(), srcStart, srcLength, options);
 }
}

inline int8_t
UnicodeString::caseCompare(const UnicodeString &text, uint32_t options) const {
 return doCaseCompare(0, length(), text, 0, text.length(), options);
}

inline int8_t
UnicodeString::caseCompare(int32_t start,
                          int32_t _length,
                          const UnicodeString &srcText,
                          uint32_t options) const {
 return doCaseCompare(start, _length, srcText, 0, srcText.length(), options);
}

inline int8_t
UnicodeString::caseCompare(ConstChar16Ptr srcChars,
                          int32_t srcLength,
                          uint32_t options) const {
 return doCaseCompare(0, length(), srcChars, 0, srcLength, options);
}

inline int8_t
UnicodeString::caseCompare(int32_t start,
                          int32_t _length,
                          const UnicodeString &srcText,
                          int32_t srcStart,
                          int32_t srcLength,
                          uint32_t options) const {
 return doCaseCompare(start, _length, srcText, srcStart, srcLength, options);
}

inline int8_t
UnicodeString::caseCompare(int32_t start,
                          int32_t _length,
                          const char16_t *srcChars,
                          uint32_t options) const {
 return doCaseCompare(start, _length, srcChars, 0, _length, options);
}

inline int8_t
UnicodeString::caseCompare(int32_t start,
                          int32_t _length,
                          const char16_t *srcChars,
                          int32_t srcStart,
                          int32_t srcLength,
                          uint32_t options) const {
 return doCaseCompare(start, _length, srcChars, srcStart, srcLength, options);
}

inline int8_t
UnicodeString::caseCompareBetween(int32_t start,
                                 int32_t limit,
                                 const UnicodeString &srcText,
                                 int32_t srcStart,
                                 int32_t srcLimit,
                                 uint32_t options) const {
 return doCaseCompare(start, limit - start, srcText, srcStart, srcLimit - srcStart, options);
}

inline int32_t
UnicodeString::indexOf(const UnicodeString& srcText,
              int32_t srcStart,
              int32_t srcLength,
              int32_t start,
              int32_t _length) const
{
 if(!srcText.isBogus()) {
   srcText.pinIndices(srcStart, srcLength);
   if(srcLength > 0) {
     return indexOf(srcText.getArrayStart(), srcStart, srcLength, start, _length);
   }
 }
 return -1;
}

inline int32_t
UnicodeString::indexOf(const UnicodeString& text) const
{ return indexOf(text, 0, text.length(), 0, length()); }

inline int32_t
UnicodeString::indexOf(const UnicodeString& text,
              int32_t start) const {
 pinIndex(start);
 return indexOf(text, 0, text.length(), start, length() - start);
}

inline int32_t
UnicodeString::indexOf(const UnicodeString& text,
              int32_t start,
              int32_t _length) const
{ return indexOf(text, 0, text.length(), start, _length); }

inline int32_t
UnicodeString::indexOf(const char16_t *srcChars,
              int32_t srcLength,
              int32_t start) const {
 pinIndex(start);
 return indexOf(srcChars, 0, srcLength, start, length() - start);
}

inline int32_t
UnicodeString::indexOf(ConstChar16Ptr srcChars,
              int32_t srcLength,
              int32_t start,
              int32_t _length) const
{ return indexOf(srcChars, 0, srcLength, start, _length); }

inline int32_t
UnicodeString::indexOf(char16_t c,
              int32_t start,
              int32_t _length) const
{ return doIndexOf(c, start, _length); }

inline int32_t
UnicodeString::indexOf(UChar32 c,
              int32_t start,
              int32_t _length) const
{ return doIndexOf(c, start, _length); }

inline int32_t
UnicodeString::indexOf(char16_t c) const
{ return doIndexOf(c, 0, length()); }

inline int32_t
UnicodeString::indexOf(UChar32 c) const
{ return indexOf(c, 0, length()); }

inline int32_t
UnicodeString::indexOf(char16_t c,
              int32_t start) const {
 pinIndex(start);
 return doIndexOf(c, start, length() - start);
}

inline int32_t
UnicodeString::indexOf(UChar32 c,
              int32_t start) const {
 pinIndex(start);
 return indexOf(c, start, length() - start);
}

inline int32_t
UnicodeString::lastIndexOf(ConstChar16Ptr srcChars,
              int32_t srcLength,
              int32_t start,
              int32_t _length) const
{ return lastIndexOf(srcChars, 0, srcLength, start, _length); }

inline int32_t
UnicodeString::lastIndexOf(const char16_t *srcChars,
              int32_t srcLength,
              int32_t start) const {
 pinIndex(start);
 return lastIndexOf(srcChars, 0, srcLength, start, length() - start);
}

inline int32_t
UnicodeString::lastIndexOf(const UnicodeString& srcText,
              int32_t srcStart,
              int32_t srcLength,
              int32_t start,
              int32_t _length) const
{
 if(!srcText.isBogus()) {
   srcText.pinIndices(srcStart, srcLength);
   if(srcLength > 0) {
     return lastIndexOf(srcText.getArrayStart(), srcStart, srcLength, start, _length);
   }
 }
 return -1;
}

inline int32_t
UnicodeString::lastIndexOf(const UnicodeString& text,
              int32_t start,
              int32_t _length) const
{ return lastIndexOf(text, 0, text.length(), start, _length); }

inline int32_t
UnicodeString::lastIndexOf(const UnicodeString& text,
              int32_t start) const {
 pinIndex(start);
 return lastIndexOf(text, 0, text.length(), start, length() - start);
}

inline int32_t
UnicodeString::lastIndexOf(const UnicodeString& text) const
{ return lastIndexOf(text, 0, text.length(), 0, length()); }

inline int32_t
UnicodeString::lastIndexOf(char16_t c,
              int32_t start,
              int32_t _length) const
{ return doLastIndexOf(c, start, _length); }

inline int32_t
UnicodeString::lastIndexOf(UChar32 c,
              int32_t start,
              int32_t _length) const {
 return doLastIndexOf(c, start, _length);
}

inline int32_t
UnicodeString::lastIndexOf(char16_t c) const
{ return doLastIndexOf(c, 0, length()); }

inline int32_t
UnicodeString::lastIndexOf(UChar32 c) const {
 return lastIndexOf(c, 0, length());
}

inline int32_t
UnicodeString::lastIndexOf(char16_t c,
              int32_t start) const {
 pinIndex(start);
 return doLastIndexOf(c, start, length() - start);
}

inline int32_t
UnicodeString::lastIndexOf(UChar32 c,
              int32_t start) const {
 pinIndex(start);
 return lastIndexOf(c, start, length() - start);
}

inline UBool
UnicodeString::startsWith(const UnicodeString& text) const
{ return doEqualsSubstring(0, text.length(), text, 0, text.length()); }

inline UBool
UnicodeString::startsWith(const UnicodeString& srcText,
             int32_t srcStart,
             int32_t srcLength) const
{ return doEqualsSubstring(0, srcLength, srcText, srcStart, srcLength); }

inline UBool
UnicodeString::startsWith(ConstChar16Ptr srcChars, int32_t srcLength) const {
 if(srcLength < 0) {
   srcLength = u_strlen(toUCharPtr(srcChars));
 }
 return doEqualsSubstring(0, srcLength, srcChars, 0, srcLength);
}

inline UBool
UnicodeString::startsWith(const char16_t *srcChars, int32_t srcStart, int32_t srcLength) const {
 if(srcLength < 0) {
   srcLength = u_strlen(toUCharPtr(srcChars));
 }
 return doEqualsSubstring(0, srcLength, srcChars, srcStart, srcLength);
}

inline UBool
UnicodeString::endsWith(const UnicodeString& text) const
{ return doEqualsSubstring(length() - text.length(), text.length(),
          text, 0, text.length()); }

inline UBool
UnicodeString::endsWith(const UnicodeString& srcText,
           int32_t srcStart,
           int32_t srcLength) const {
 srcText.pinIndices(srcStart, srcLength);
 return doEqualsSubstring(length() - srcLength, srcLength,
                  srcText, srcStart, srcLength);
}

inline UBool
UnicodeString::endsWith(ConstChar16Ptr srcChars,
           int32_t srcLength) const {
 if(srcLength < 0) {
   srcLength = u_strlen(toUCharPtr(srcChars));
 }
 return doEqualsSubstring(length() - srcLength, srcLength, srcChars, 0, srcLength);
}

inline UBool
UnicodeString::endsWith(const char16_t *srcChars,
           int32_t srcStart,
           int32_t srcLength) const {
 if(srcLength < 0) {
   srcLength = u_strlen(toUCharPtr(srcChars + srcStart));
 }
 return doEqualsSubstring(length() - srcLength, srcLength,
                  srcChars, srcStart, srcLength);
}

//========================================
// replace
//========================================
inline UnicodeString&
UnicodeString::replace(int32_t start,
              int32_t _length,
              const UnicodeString& srcText)
{ return doReplace(start, _length, srcText, 0, srcText.length()); }

inline UnicodeString&
UnicodeString::replace(int32_t start,
              int32_t _length,
              const UnicodeString& srcText,
              int32_t srcStart,
              int32_t srcLength)
{ return doReplace(start, _length, srcText, srcStart, srcLength); }

inline UnicodeString&
UnicodeString::replace(int32_t start,
              int32_t _length,
              ConstChar16Ptr srcChars,
              int32_t srcLength)
{ return doReplace(start, _length, srcChars, 0, srcLength); }

inline UnicodeString&
UnicodeString::replace(int32_t start,
              int32_t _length,
              const char16_t *srcChars,
              int32_t srcStart,
              int32_t srcLength)
{ return doReplace(start, _length, srcChars, srcStart, srcLength); }

inline UnicodeString&
UnicodeString::replace(int32_t start,
              int32_t _length,
              char16_t srcChar)
{ return doReplace(start, _length, &srcChar, 0, 1); }

inline UnicodeString&
UnicodeString::replaceBetween(int32_t start,
                 int32_t limit,
                 const UnicodeString& srcText)
{ return doReplace(start, limit - start, srcText, 0, srcText.length()); }

inline UnicodeString&
UnicodeString::replaceBetween(int32_t start,
                 int32_t limit,
                 const UnicodeString& srcText,
                 int32_t srcStart,
                 int32_t srcLimit)
{ return doReplace(start, limit - start, srcText, srcStart, srcLimit - srcStart); }

inline UnicodeString&
UnicodeString::findAndReplace(const UnicodeString& oldText,
                 const UnicodeString& newText)
{ return findAndReplace(0, length(), oldText, 0, oldText.length(),
           newText, 0, newText.length()); }

inline UnicodeString&
UnicodeString::findAndReplace(int32_t start,
                 int32_t _length,
                 const UnicodeString& oldText,
                 const UnicodeString& newText)
{ return findAndReplace(start, _length, oldText, 0, oldText.length(),
           newText, 0, newText.length()); }

// ============================
// extract
// ============================
inline void
UnicodeString::doExtract(int32_t start,
            int32_t _length,
            UnicodeString& target) const
{ target.replace(0, target.length(), *this, start, _length); }

inline void
UnicodeString::extract(int32_t start,
              int32_t _length,
              Char16Ptr target,
              int32_t targetStart) const
{ doExtract(start, _length, target, targetStart); }

inline void
UnicodeString::extract(int32_t start,
              int32_t _length,
              UnicodeString& target) const
{ doExtract(start, _length, target); }

#if !UCONFIG_NO_CONVERSION

inline int32_t
UnicodeString::extract(int32_t start,
              int32_t _length,
              char *dst,
              const char *codepage) const

{
 // This dstSize value will be checked explicitly
 return extract(start, _length, dst, dst != nullptr ? 0xffffffff : 0, codepage);
}

#endif

inline void
UnicodeString::extractBetween(int32_t start,
                 int32_t limit,
                 char16_t *dst,
                 int32_t dstStart) const {
 pinIndex(start);
 pinIndex(limit);
 doExtract(start, limit - start, dst, dstStart);
}

inline UnicodeString
UnicodeString::tempSubStringBetween(int32_t start, int32_t limit) const {
   return tempSubString(start, limit - start);
}

inline char16_t
UnicodeString::doCharAt(int32_t offset) const
{
 if (static_cast<uint32_t>(offset) < static_cast<uint32_t>(length())) {
   return getArrayStart()[offset];
 } else {
   return kInvalidUChar;
 }
}

inline char16_t
UnicodeString::charAt(int32_t offset) const
{ return doCharAt(offset); }

inline char16_t
UnicodeString::operator[] (int32_t offset) const
{ return doCharAt(offset); }

inline UBool
UnicodeString::isEmpty() const {
 // Arithmetic or logical right shift does not matter: only testing for 0.
 return (fUnion.fFields.fLengthAndFlags>>kLengthShift) == 0;
}

//========================================
// Write implementation methods
//========================================
inline void
UnicodeString::setZeroLength() {
 fUnion.fFields.fLengthAndFlags &= kAllStorageFlags;
}

inline void
UnicodeString::setShortLength(int32_t len) {
 // requires 0 <= len <= kMaxShortLength
 fUnion.fFields.fLengthAndFlags =
   static_cast<int16_t>((fUnion.fFields.fLengthAndFlags & kAllStorageFlags) | (len << kLengthShift));
}

inline void
UnicodeString::setLength(int32_t len) {
 if(len <= kMaxShortLength) {
   setShortLength(len);
 } else {
   fUnion.fFields.fLengthAndFlags |= kLengthIsLarge;
   fUnion.fFields.fLength = len;
 }
}

inline void
UnicodeString::setToEmpty() {
 fUnion.fFields.fLengthAndFlags = kShortString;
}

inline void
UnicodeString::setArray(char16_t *array, int32_t len, int32_t capacity) {
 setLength(len);
 fUnion.fFields.fArray = array;
 fUnion.fFields.fCapacity = capacity;
}

inline UnicodeString&
UnicodeString::operator= (char16_t ch)
{ return doReplace(0, length(), &ch, 0, 1); }

inline UnicodeString&
UnicodeString::operator= (UChar32 ch)
{ return replace(0, length(), ch); }

inline UnicodeString&
UnicodeString::setTo(const UnicodeString& srcText,
            int32_t srcStart,
            int32_t srcLength)
{
 unBogus();
 return doReplace(0, length(), srcText, srcStart, srcLength);
}

inline UnicodeString&
UnicodeString::setTo(const UnicodeString& srcText,
            int32_t srcStart)
{
 unBogus();
 srcText.pinIndex(srcStart);
 return doReplace(0, length(), srcText, srcStart, srcText.length() - srcStart);
}

inline UnicodeString&
UnicodeString::setTo(const UnicodeString& srcText)
{
 return copyFrom(srcText);
}

inline UnicodeString&
UnicodeString::setTo(const char16_t *srcChars,
            int32_t srcLength)
{
 unBogus();
 return doReplace(0, length(), srcChars, 0, srcLength);
}

inline UnicodeString&
UnicodeString::setTo(char16_t srcChar)
{
 unBogus();
 return doReplace(0, length(), &srcChar, 0, 1);
}

inline UnicodeString&
UnicodeString::setTo(UChar32 srcChar)
{
 unBogus();
 return replace(0, length(), srcChar);
}

inline UnicodeString&
UnicodeString::append(const UnicodeString& srcText,
             int32_t srcStart,
             int32_t srcLength)
{ return doAppend(srcText, srcStart, srcLength); }

inline UnicodeString&
UnicodeString::append(const UnicodeString& srcText)
{ return doAppend(srcText, 0, srcText.length()); }

inline UnicodeString&
UnicodeString::append(const char16_t *srcChars,
             int32_t srcStart,
             int32_t srcLength)
{ return doAppend(srcChars, srcStart, srcLength); }

inline UnicodeString&
UnicodeString::append(ConstChar16Ptr srcChars,
             int32_t srcLength)
{ return doAppend(srcChars, 0, srcLength); }

inline UnicodeString&
UnicodeString::append(char16_t srcChar)
{ return doAppend(&srcChar, 0, 1); }

inline UnicodeString&
UnicodeString::operator+= (char16_t ch)
{ return doAppend(&ch, 0, 1); }

inline UnicodeString&
UnicodeString::operator+= (UChar32 ch) {
 return append(ch);
}

inline UnicodeString&
UnicodeString::operator+= (const UnicodeString& srcText)
{ return doAppend(srcText, 0, srcText.length()); }

inline UnicodeString&
UnicodeString::insert(int32_t start,
             const UnicodeString& srcText,
             int32_t srcStart,
             int32_t srcLength)
{ return doReplace(start, 0, srcText, srcStart, srcLength); }

inline UnicodeString&
UnicodeString::insert(int32_t start,
             const UnicodeString& srcText)
{ return doReplace(start, 0, srcText, 0, srcText.length()); }

inline UnicodeString&
UnicodeString::insert(int32_t start,
             const char16_t *srcChars,
             int32_t srcStart,
             int32_t srcLength)
{ return doReplace(start, 0, srcChars, srcStart, srcLength); }

inline UnicodeString&
UnicodeString::insert(int32_t start,
             ConstChar16Ptr srcChars,
             int32_t srcLength)
{ return doReplace(start, 0, srcChars, 0, srcLength); }

inline UnicodeString&
UnicodeString::insert(int32_t start,
             char16_t srcChar)
{ return doReplace(start, 0, &srcChar, 0, 1); }

inline UnicodeString&
UnicodeString::insert(int32_t start,
             UChar32 srcChar)
{ return replace(start, 0, srcChar); }


inline UnicodeString&
UnicodeString::remove()
{
 // remove() of a bogus string makes the string empty and non-bogus
 if(isBogus()) {
   setToEmpty();
 } else {
   setZeroLength();
 }
 return *this;
}

inline UnicodeString&
UnicodeString::remove(int32_t start,
            int32_t _length)
{
   if(start <= 0 && _length == INT32_MAX) {
       // remove(guaranteed everything) of a bogus string makes the string empty and non-bogus
       return remove();
   }
   return doReplace(start, _length, nullptr, 0, 0);
}

inline UnicodeString&
UnicodeString::removeBetween(int32_t start,
               int32_t limit)
{ return doReplace(start, limit - start, nullptr, 0, 0); }

inline UnicodeString &
UnicodeString::retainBetween(int32_t start, int32_t limit) {
 truncate(limit);
 return doReplace(0, start, nullptr, 0, 0);
}

inline UBool
UnicodeString::truncate(int32_t targetLength)
{
 if(isBogus() && targetLength == 0) {
   // truncate(0) of a bogus string makes the string empty and non-bogus
   unBogus();
   return false;
 } else if (static_cast<uint32_t>(targetLength) < static_cast<uint32_t>(length())) {
   setLength(targetLength);
   return true;
 } else {
   return false;
 }
}

inline UnicodeString&
UnicodeString::reverse()
{ return doReverse(0, length()); }

inline UnicodeString&
UnicodeString::reverse(int32_t start,
              int32_t _length)
{ return doReverse(start, _length); }

U_NAMESPACE_END

#endif /* U_SHOW_CPLUSPLUS_API */

#endif