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string_view.h (29699B)

---

//
// Copyright 2017 The Abseil Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//      https://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//
// -----------------------------------------------------------------------------
// File: string_view.h
// -----------------------------------------------------------------------------
//
// This file contains the definition of the `absl::string_view` class. A
// `string_view` points to a contiguous span of characters, often part or all of
// another `std::string`, double-quoted string literal, character array, or even
// another `string_view`.
//
// This `absl::string_view` abstraction is designed to be a drop-in
// replacement for the C++17 `std::string_view` abstraction.
#ifndef ABSL_STRINGS_STRING_VIEW_H_
#define ABSL_STRINGS_STRING_VIEW_H_

#include <algorithm>
#include <cassert>
#include <cstddef>
#include <cstring>
#include <iosfwd>
#include <iterator>
#include <limits>
#include <string>

#include "absl/base/attributes.h"
#include "absl/base/nullability.h"
#include "absl/base/config.h"
#include "absl/base/internal/throw_delegate.h"
#include "absl/base/macros.h"
#include "absl/base/optimization.h"
#include "absl/base/port.h"

#ifdef ABSL_USES_STD_STRING_VIEW

#include <string_view>  // IWYU pragma: export

namespace absl {
ABSL_NAMESPACE_BEGIN
using string_view = std::string_view;
ABSL_NAMESPACE_END
}  // namespace absl

#else  // ABSL_USES_STD_STRING_VIEW

#if ABSL_HAVE_BUILTIN(__builtin_memcmp) ||        \
   (defined(__GNUC__) && !defined(__clang__)) || \
   (defined(_MSC_VER) && _MSC_VER >= 1928)
#define ABSL_INTERNAL_STRING_VIEW_MEMCMP __builtin_memcmp
#else  // ABSL_HAVE_BUILTIN(__builtin_memcmp)
#define ABSL_INTERNAL_STRING_VIEW_MEMCMP memcmp
#endif  // ABSL_HAVE_BUILTIN(__builtin_memcmp)

namespace absl {
ABSL_NAMESPACE_BEGIN

// Mozilla added - quiets misused comma warnings resulting from
// frequent use of the pattern:
//     return ABSL_HARDENING_ASSERT(i < size()), ptr_[i];
// TODO: https://bugzilla.mozilla.org/show_bug.cgi?id=1796623
#if defined(__clang__)
#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Wcomma"
#endif

// absl::string_view
//
// A `string_view` provides a lightweight view into the string data provided by
// a `std::string`, double-quoted string literal, character array, or even
// another `string_view`. A `string_view` does *not* own the string to which it
// points, and that data cannot be modified through the view.
//
// You can use `string_view` as a function or method parameter anywhere a
// parameter can receive a double-quoted string literal, `const char*`,
// `std::string`, or another `absl::string_view` argument with no need to copy
// the string data. Systematic use of `string_view` within function arguments
// reduces data copies and `strlen()` calls.
//
// Because of its small size, prefer passing `string_view` by value:
//
//   void MyFunction(absl::string_view arg);
//
// If circumstances require, you may also pass one by const reference:
//
//   void MyFunction(const absl::string_view& arg);  // not preferred
//
// Passing by value generates slightly smaller code for many architectures.
//
// In either case, the source data of the `string_view` must outlive the
// `string_view` itself.
//
// A `string_view` is also suitable for local variables if you know that the
// lifetime of the underlying object is longer than the lifetime of your
// `string_view` variable. However, beware of binding a `string_view` to a
// temporary value:
//
//   // BAD use of string_view: lifetime problem
//   absl::string_view sv = obj.ReturnAString();
//
//   // GOOD use of string_view: str outlives sv
//   std::string str = obj.ReturnAString();
//   absl::string_view sv = str;
//
// Due to lifetime issues, a `string_view` is sometimes a poor choice for a
// return value and usually a poor choice for a data member. If you do use a
// `string_view` this way, it is your responsibility to ensure that the object
// pointed to by the `string_view` outlives the `string_view`.
//
// A `string_view` may represent a whole string or just part of a string. For
// example, when splitting a string, `std::vector<absl::string_view>` is a
// natural data type for the output.
//
// For another example, a Cord is a non-contiguous, potentially very
// long string-like object.  The Cord class has an interface that iteratively
// provides string_view objects that point to the successive pieces of a Cord
// object.
//
// When constructed from a source which is NUL-terminated, the `string_view`
// itself will not include the NUL-terminator unless a specific size (including
// the NUL) is passed to the constructor. As a result, common idioms that work
// on NUL-terminated strings do not work on `string_view` objects. If you write
// code that scans a `string_view`, you must check its length rather than test
// for nul, for example. Note, however, that nuls may still be embedded within
// a `string_view` explicitly.
//
// You may create a null `string_view` in two ways:
//
//   absl::string_view sv;
//   absl::string_view sv(nullptr, 0);
//
// For the above, `sv.data() == nullptr`, `sv.length() == 0`, and
// `sv.empty() == true`. Also, if you create a `string_view` with a non-null
// pointer then `sv.data() != nullptr`. Thus, you can use `string_view()` to
// signal an undefined value that is different from other `string_view` values
// in a similar fashion to how `const char* p1 = nullptr;` is different from
// `const char* p2 = "";`. However, in practice, it is not recommended to rely
// on this behavior.
//
// Be careful not to confuse a null `string_view` with an empty one. A null
// `string_view` is an empty `string_view`, but some empty `string_view`s are
// not null. Prefer checking for emptiness over checking for null.
//
// There are many ways to create an empty string_view:
//
//   const char* nullcp = nullptr;
//   // string_view.size() will return 0 in all cases.
//   absl::string_view();
//   absl::string_view(nullcp, 0);
//   absl::string_view("");
//   absl::string_view("", 0);
//   absl::string_view("abcdef", 0);
//   absl::string_view("abcdef" + 6, 0);
//
// All empty `string_view` objects whether null or not, are equal:
//
//   absl::string_view() == absl::string_view("", 0)
//   absl::string_view(nullptr, 0) == absl::string_view("abcdef"+6, 0)
class ABSL_ATTRIBUTE_VIEW string_view {
public:
 using traits_type = std::char_traits<char>;
 using value_type = char;
 using pointer = absl::Nullable<char*>;
 using const_pointer = absl::Nullable<const char*>;
 using reference = char&;
 using const_reference = const char&;
 using const_iterator = absl::Nullable<const char*>;
 using iterator = const_iterator;
 using const_reverse_iterator = std::reverse_iterator<const_iterator>;
 using reverse_iterator = const_reverse_iterator;
 using size_type = size_t;
 using difference_type = std::ptrdiff_t;
 using absl_internal_is_view = std::true_type;

 static constexpr size_type npos = static_cast<size_type>(-1);

 // Null `string_view` constructor
 constexpr string_view() noexcept : ptr_(nullptr), length_(0) {}

 // Implicit constructors

 template <typename Allocator>
 string_view(  // NOLINT(runtime/explicit)
     const std::basic_string<char, std::char_traits<char>, Allocator>& str
         ABSL_ATTRIBUTE_LIFETIME_BOUND) noexcept
     // This is implemented in terms of `string_view(p, n)` so `str.size()`
     // doesn't need to be reevaluated after `ptr_` is set.
     // The length check is also skipped since it is unnecessary and causes
     // code bloat.
     : string_view(str.data(), str.size(), SkipCheckLengthTag{}) {}

 // Implicit constructor of a `string_view` from NUL-terminated `str`. When
 // accepting possibly null strings, use `absl::NullSafeStringView(str)`
 // instead (see below).
 // The length check is skipped since it is unnecessary and causes code bloat.
 constexpr string_view(  // NOLINT(runtime/explicit)
     absl::Nonnull<const char*> str)
     : ptr_(str), length_(str ? StrlenInternal(str) : 0) {}

 // Constructor of a `string_view` from a `const char*` and length.
 constexpr string_view(absl::Nullable<const char*> data, size_type len)
     : ptr_(data), length_(CheckLengthInternal(len)) {}

 constexpr string_view(const string_view&) noexcept = default;
 string_view& operator=(const string_view&) noexcept = default;

 // Iterators

 // string_view::begin()
 //
 // Returns an iterator pointing to the first character at the beginning of the
 // `string_view`, or `end()` if the `string_view` is empty.
 constexpr const_iterator begin() const noexcept { return ptr_; }

 // string_view::end()
 //
 // Returns an iterator pointing just beyond the last character at the end of
 // the `string_view`. This iterator acts as a placeholder; attempting to
 // access it results in undefined behavior.
 constexpr const_iterator end() const noexcept { return ptr_ + length_; }

 // string_view::cbegin()
 //
 // Returns a const iterator pointing to the first character at the beginning
 // of the `string_view`, or `end()` if the `string_view` is empty.
 constexpr const_iterator cbegin() const noexcept { return begin(); }

 // string_view::cend()
 //
 // Returns a const iterator pointing just beyond the last character at the end
 // of the `string_view`. This pointer acts as a placeholder; attempting to
 // access its element results in undefined behavior.
 constexpr const_iterator cend() const noexcept { return end(); }

 // string_view::rbegin()
 //
 // Returns a reverse iterator pointing to the last character at the end of the
 // `string_view`, or `rend()` if the `string_view` is empty.
 const_reverse_iterator rbegin() const noexcept {
   return const_reverse_iterator(end());
 }

 // string_view::rend()
 //
 // Returns a reverse iterator pointing just before the first character at the
 // beginning of the `string_view`. This pointer acts as a placeholder;
 // attempting to access its element results in undefined behavior.
 const_reverse_iterator rend() const noexcept {
   return const_reverse_iterator(begin());
 }

 // string_view::crbegin()
 //
 // Returns a const reverse iterator pointing to the last character at the end
 // of the `string_view`, or `crend()` if the `string_view` is empty.
 const_reverse_iterator crbegin() const noexcept { return rbegin(); }

 // string_view::crend()
 //
 // Returns a const reverse iterator pointing just before the first character
 // at the beginning of the `string_view`. This pointer acts as a placeholder;
 // attempting to access its element results in undefined behavior.
 const_reverse_iterator crend() const noexcept { return rend(); }

 // Capacity Utilities

 // string_view::size()
 //
 // Returns the number of characters in the `string_view`.
 constexpr size_type size() const noexcept { return length_; }

 // string_view::length()
 //
 // Returns the number of characters in the `string_view`. Alias for `size()`.
 constexpr size_type length() const noexcept { return size(); }

 // string_view::max_size()
 //
 // Returns the maximum number of characters the `string_view` can hold.
 constexpr size_type max_size() const noexcept { return kMaxSize; }

 // string_view::empty()
 //
 // Checks if the `string_view` is empty (refers to no characters).
 constexpr bool empty() const noexcept { return length_ == 0; }

 // string_view::operator[]
 //
 // Returns the ith element of the `string_view` using the array operator.
 // Note that this operator does not perform any bounds checking.
 constexpr const_reference operator[](size_type i) const {
   ABSL_HARDENING_ASSERT(i < size());
   return ptr_[i];
 }

 // string_view::at()
 //
 // Returns the ith element of the `string_view`. Bounds checking is performed,
 // and an exception of type `std::out_of_range` will be thrown on invalid
 // access.
 constexpr const_reference at(size_type i) const {
   if (ABSL_PREDICT_FALSE(i >= size())) {
     base_internal::ThrowStdOutOfRange("absl::string_view::at");
   }
   return ptr_[i];
 }

 // string_view::front()
 //
 // Returns the first element of a `string_view`.
 constexpr const_reference front() const {
   ABSL_HARDENING_ASSERT(!empty());
   return ptr_[0];
 }

 // string_view::back()
 //
 // Returns the last element of a `string_view`.
 constexpr const_reference back() const {
   ABSL_HARDENING_ASSERT(!empty());
   return ptr_[size() - 1];
 }

 // string_view::data()
 //
 // Returns a pointer to the underlying character array (which is of course
 // stored elsewhere). Note that `string_view::data()` may contain embedded nul
 // characters, but the returned buffer may or may not be NUL-terminated;
 // therefore, do not pass `data()` to a routine that expects a NUL-terminated
 // string.
 constexpr const_pointer data() const noexcept { return ptr_; }

 // Modifiers

 // string_view::remove_prefix()
 //
 // Removes the first `n` characters from the `string_view`. Note that the
 // underlying string is not changed, only the view.
 constexpr void remove_prefix(size_type n) {
   ABSL_HARDENING_ASSERT(n <= length_);
   ptr_ += n;
   length_ -= n;
 }

 // string_view::remove_suffix()
 //
 // Removes the last `n` characters from the `string_view`. Note that the
 // underlying string is not changed, only the view.
 constexpr void remove_suffix(size_type n) {
   ABSL_HARDENING_ASSERT(n <= length_);
   length_ -= n;
 }

 // string_view::swap()
 //
 // Swaps this `string_view` with another `string_view`.
 constexpr void swap(string_view& s) noexcept {
   auto t = *this;
   *this = s;
   s = t;
 }

 // Explicit conversion operators

 // Converts to `std::basic_string`.
 template <typename A>
 explicit operator std::basic_string<char, traits_type, A>() const {
   if (!data()) return {};
   return std::basic_string<char, traits_type, A>(data(), size());
 }

 // string_view::copy()
 //
 // Copies the contents of the `string_view` at offset `pos` and length `n`
 // into `buf`.
 size_type copy(char* buf, size_type n, size_type pos = 0) const {
   if (ABSL_PREDICT_FALSE(pos > length_)) {
     base_internal::ThrowStdOutOfRange("absl::string_view::copy");
   }
   size_type rlen = (std::min)(length_ - pos, n);
   if (rlen > 0) {
     const char* start = ptr_ + pos;
     traits_type::copy(buf, start, rlen);
   }
   return rlen;
 }

 // string_view::substr()
 //
 // Returns a "substring" of the `string_view` (at offset `pos` and length
 // `n`) as another string_view. This function throws `std::out_of_bounds` if
 // `pos > size`.
 // Use absl::ClippedSubstr if you need a truncating substr operation.
 constexpr string_view substr(size_type pos = 0, size_type n = npos) const {
   if (ABSL_PREDICT_FALSE(pos > length_)) {
     base_internal::ThrowStdOutOfRange("absl::string_view::substr");
   }
   return string_view(ptr_ + pos, (std::min)(n, length_ - pos));
 }

 // string_view::compare()
 //
 // Performs a lexicographical comparison between this `string_view` and
 // another `string_view` `x`, returning a negative value if `*this` is less
 // than `x`, 0 if `*this` is equal to `x`, and a positive value if `*this`
 // is greater than `x`.
 constexpr int compare(string_view x) const noexcept {
   return CompareImpl(length_, x.length_,
                      (std::min)(length_, x.length_) == 0
                          ? 0
                          : ABSL_INTERNAL_STRING_VIEW_MEMCMP(
                                ptr_, x.ptr_, (std::min)(length_, x.length_)));
 }

 // Overload of `string_view::compare()` for comparing a substring of the
 // 'string_view` and another `absl::string_view`.
 constexpr int compare(size_type pos1, size_type count1, string_view v) const {
   return substr(pos1, count1).compare(v);
 }

 // Overload of `string_view::compare()` for comparing a substring of the
 // `string_view` and a substring of another `absl::string_view`.
 constexpr int compare(size_type pos1, size_type count1, string_view v,
                       size_type pos2, size_type count2) const {
   return substr(pos1, count1).compare(v.substr(pos2, count2));
 }

 // Overload of `string_view::compare()` for comparing a `string_view` and a
 // a different C-style string `s`.
 constexpr int compare(absl::Nonnull<const char*> s) const {
   return compare(string_view(s));
 }

 // Overload of `string_view::compare()` for comparing a substring of the
 // `string_view` and a different string C-style string `s`.
 constexpr int compare(size_type pos1, size_type count1,
                       absl::Nonnull<const char*> s) const {
   return substr(pos1, count1).compare(string_view(s));
 }

 // Overload of `string_view::compare()` for comparing a substring of the
 // `string_view` and a substring of a different C-style string `s`.
 constexpr int compare(size_type pos1, size_type count1,
                       absl::Nonnull<const char*> s, size_type count2) const {
   return substr(pos1, count1).compare(string_view(s, count2));
 }

 // Find Utilities

 // string_view::find()
 //
 // Finds the first occurrence of the substring `s` within the `string_view`,
 // returning the position of the first character's match, or `npos` if no
 // match was found.
 size_type find(string_view s, size_type pos = 0) const noexcept;

 // Overload of `string_view::find()` for finding the given character `c`
 // within the `string_view`.
 size_type find(char c, size_type pos = 0) const noexcept;

 // Overload of `string_view::find()` for finding a substring of a different
 // C-style string `s` within the `string_view`.
 size_type find(absl::Nonnull<const char*> s, size_type pos,
                size_type count) const {
   return find(string_view(s, count), pos);
 }

 // Overload of `string_view::find()` for finding a different C-style string
 // `s` within the `string_view`.
 size_type find(absl::Nonnull<const char *> s, size_type pos = 0) const {
   return find(string_view(s), pos);
 }

 // string_view::rfind()
 //
 // Finds the last occurrence of a substring `s` within the `string_view`,
 // returning the position of the first character's match, or `npos` if no
 // match was found.
 size_type rfind(string_view s, size_type pos = npos) const noexcept;

 // Overload of `string_view::rfind()` for finding the last given character `c`
 // within the `string_view`.
 size_type rfind(char c, size_type pos = npos) const noexcept;

 // Overload of `string_view::rfind()` for finding a substring of a different
 // C-style string `s` within the `string_view`.
 size_type rfind(absl::Nonnull<const char*> s, size_type pos,
                 size_type count) const {
   return rfind(string_view(s, count), pos);
 }

 // Overload of `string_view::rfind()` for finding a different C-style string
 // `s` within the `string_view`.
 size_type rfind(absl::Nonnull<const char*> s, size_type pos = npos) const {
   return rfind(string_view(s), pos);
 }

 // string_view::find_first_of()
 //
 // Finds the first occurrence of any of the characters in `s` within the
 // `string_view`, returning the start position of the match, or `npos` if no
 // match was found.
 size_type find_first_of(string_view s, size_type pos = 0) const noexcept;

 // Overload of `string_view::find_first_of()` for finding a character `c`
 // within the `string_view`.
 size_type find_first_of(char c, size_type pos = 0) const noexcept {
   return find(c, pos);
 }

 // Overload of `string_view::find_first_of()` for finding a substring of a
 // different C-style string `s` within the `string_view`.
 size_type find_first_of(absl::Nonnull<const char*> s, size_type pos,
                         size_type count) const {
   return find_first_of(string_view(s, count), pos);
 }

 // Overload of `string_view::find_first_of()` for finding a different C-style
 // string `s` within the `string_view`.
 size_type find_first_of(absl::Nonnull<const char*> s,
                         size_type pos = 0) const {
   return find_first_of(string_view(s), pos);
 }

 // string_view::find_last_of()
 //
 // Finds the last occurrence of any of the characters in `s` within the
 // `string_view`, returning the start position of the match, or `npos` if no
 // match was found.
 size_type find_last_of(string_view s, size_type pos = npos) const noexcept;

 // Overload of `string_view::find_last_of()` for finding a character `c`
 // within the `string_view`.
 size_type find_last_of(char c, size_type pos = npos) const noexcept {
   return rfind(c, pos);
 }

 // Overload of `string_view::find_last_of()` for finding a substring of a
 // different C-style string `s` within the `string_view`.
 size_type find_last_of(absl::Nonnull<const char*> s, size_type pos,
                        size_type count) const {
   return find_last_of(string_view(s, count), pos);
 }

 // Overload of `string_view::find_last_of()` for finding a different C-style
 // string `s` within the `string_view`.
 size_type find_last_of(absl::Nonnull<const char*> s,
                        size_type pos = npos) const {
   return find_last_of(string_view(s), pos);
 }

 // string_view::find_first_not_of()
 //
 // Finds the first occurrence of any of the characters not in `s` within the
 // `string_view`, returning the start position of the first non-match, or
 // `npos` if no non-match was found.
 size_type find_first_not_of(string_view s, size_type pos = 0) const noexcept;

 // Overload of `string_view::find_first_not_of()` for finding a character
 // that is not `c` within the `string_view`.
 size_type find_first_not_of(char c, size_type pos = 0) const noexcept;

 // Overload of `string_view::find_first_not_of()` for finding a substring of a
 // different C-style string `s` within the `string_view`.
 size_type find_first_not_of(absl::Nonnull<const char*> s, size_type pos,
                             size_type count) const {
   return find_first_not_of(string_view(s, count), pos);
 }

 // Overload of `string_view::find_first_not_of()` for finding a different
 // C-style string `s` within the `string_view`.
 size_type find_first_not_of(absl::Nonnull<const char*> s,
                             size_type pos = 0) const {
   return find_first_not_of(string_view(s), pos);
 }

 // string_view::find_last_not_of()
 //
 // Finds the last occurrence of any of the characters not in `s` within the
 // `string_view`, returning the start position of the last non-match, or
 // `npos` if no non-match was found.
 size_type find_last_not_of(string_view s,
                            size_type pos = npos) const noexcept;

 // Overload of `string_view::find_last_not_of()` for finding a character
 // that is not `c` within the `string_view`.
 size_type find_last_not_of(char c, size_type pos = npos) const noexcept;

 // Overload of `string_view::find_last_not_of()` for finding a substring of a
 // different C-style string `s` within the `string_view`.
 size_type find_last_not_of(absl::Nonnull<const char*> s, size_type pos,
                            size_type count) const {
   return find_last_not_of(string_view(s, count), pos);
 }

 // Overload of `string_view::find_last_not_of()` for finding a different
 // C-style string `s` within the `string_view`.
 size_type find_last_not_of(absl::Nonnull<const char*> s,
                            size_type pos = npos) const {
   return find_last_not_of(string_view(s), pos);
 }

#if ABSL_INTERNAL_CPLUSPLUS_LANG >= 202002L
 // string_view::starts_with()
 //
 // Returns true if the `string_view` starts with the prefix `s`.
 //
 // This method only exists when targeting at least C++20.
 // If support for C++ prior to C++20 is required, use `absl::StartsWith()`
 // from `//absl/strings/match.h` for compatibility.
 constexpr bool starts_with(string_view s) const noexcept {
   return s.empty() ||
          (size() >= s.size() &&
           ABSL_INTERNAL_STRING_VIEW_MEMCMP(data(), s.data(), s.size()) == 0);
 }

 // Overload of `string_view::starts_with()` that returns true if `c` is the
 // first character of the `string_view`.
 constexpr bool starts_with(char c) const noexcept {
   return !empty() && front() == c;
 }

 // Overload of `string_view::starts_with()` that returns true if the
 // `string_view` starts with the C-style prefix `s`.
 constexpr bool starts_with(const char* s) const {
   return starts_with(string_view(s));
 }

 // string_view::ends_with()
 //
 // Returns true if the `string_view` ends with the suffix `s`.
 //
 // This method only exists when targeting at least C++20.
 // If support for C++ prior to C++20 is required, use `absl::EndsWith()`
 // from `//absl/strings/match.h` for compatibility.
 constexpr bool ends_with(string_view s) const noexcept {
   return s.empty() || (size() >= s.size() && ABSL_INTERNAL_STRING_VIEW_MEMCMP(
                                                  data() + (size() - s.size()),
                                                  s.data(), s.size()) == 0);
 }

 // Overload of `string_view::ends_with()` that returns true if `c` is the
 // last character of the `string_view`.
 constexpr bool ends_with(char c) const noexcept {
   return !empty() && back() == c;
 }

 // Overload of `string_view::ends_with()` that returns true if the
 // `string_view` ends with the C-style suffix `s`.
 constexpr bool ends_with(const char* s) const {
   return ends_with(string_view(s));
 }
#endif  // ABSL_INTERNAL_CPLUSPLUS_LANG >= 202002L

private:
 // The constructor from std::string delegates to this constructor.
 // See the comment on that constructor for the rationale.
 struct SkipCheckLengthTag {};
 string_view(absl::Nullable<const char*> data, size_type len,
             SkipCheckLengthTag) noexcept
     : ptr_(data), length_(len) {}

 static constexpr size_type kMaxSize =
     (std::numeric_limits<difference_type>::max)();

 static constexpr size_type CheckLengthInternal(size_type len) {
   ABSL_HARDENING_ASSERT(len <= kMaxSize);
   return len;
 }

 static constexpr size_type StrlenInternal(absl::Nonnull<const char*> str) {
#if defined(_MSC_VER) && !defined(__clang__)
   // MSVC 2017+ can evaluate this at compile-time.
   const char* begin = str;
   while (*str != '\0') ++str;
   return str - begin;
#elif ABSL_HAVE_BUILTIN(__builtin_strlen) || \
   (defined(__GNUC__) && !defined(__clang__))
   // GCC has __builtin_strlen according to
   // https://gcc.gnu.org/onlinedocs/gcc-4.7.0/gcc/Other-Builtins.html, but
   // ABSL_HAVE_BUILTIN doesn't detect that, so we use the extra checks above.
   // __builtin_strlen is constexpr.
   return __builtin_strlen(str);
#else
   return str ? strlen(str) : 0;
#endif
 }

 static constexpr int CompareImpl(size_type length_a, size_type length_b,
                                  int compare_result) {
   return compare_result == 0 ? static_cast<int>(length_a > length_b) -
                                    static_cast<int>(length_a < length_b)
                              : (compare_result < 0 ? -1 : 1);
 }

 absl::Nullable<const char*> ptr_;
 size_type length_;
};

// This large function is defined inline so that in a fairly common case where
// one of the arguments is a literal, the compiler can elide a lot of the
// following comparisons.
constexpr bool operator==(string_view x, string_view y) noexcept {
 return x.size() == y.size() &&
        (x.empty() ||
         ABSL_INTERNAL_STRING_VIEW_MEMCMP(x.data(), y.data(), x.size()) == 0);
}

constexpr bool operator!=(string_view x, string_view y) noexcept {
 return !(x == y);
}

constexpr bool operator<(string_view x, string_view y) noexcept {
 return x.compare(y) < 0;
}

constexpr bool operator>(string_view x, string_view y) noexcept {
 return y < x;
}

constexpr bool operator<=(string_view x, string_view y) noexcept {
 return !(y < x);
}

constexpr bool operator>=(string_view x, string_view y) noexcept {
 return !(x < y);
}

// IO Insertion Operator
std::ostream& operator<<(std::ostream& o, string_view piece);

ABSL_NAMESPACE_END
}  // namespace absl

#undef ABSL_INTERNAL_STRING_VIEW_MEMCMP

#if defined(__clang__)
#pragma clang diagnostic pop
#endif

#endif  // ABSL_USES_STD_STRING_VIEW

namespace absl {
ABSL_NAMESPACE_BEGIN

// ClippedSubstr()
//
// Like `s.substr(pos, n)`, but clips `pos` to an upper bound of `s.size()`.
// Provided because std::string_view::substr throws if `pos > size()`
inline string_view ClippedSubstr(string_view s, size_t pos,
                                size_t n = string_view::npos) {
 pos = (std::min)(pos, static_cast<size_t>(s.size()));
 return s.substr(pos, n);
}

// NullSafeStringView()
//
// Creates an `absl::string_view` from a pointer `p` even if it's null-valued.
// This function should be used where an `absl::string_view` can be created from
// a possibly-null pointer.
constexpr string_view NullSafeStringView(absl::Nullable<const char*> p) {
 return p ? string_view(p) : string_view();
}

ABSL_NAMESPACE_END
}  // namespace absl

#endif  // ABSL_STRINGS_STRING_VIEW_H_