MacroArgs.h (3739B)
1 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */ 2 /* vim: set ts=8 sts=2 et sw=2 tw=80: */ 3 /* This Source Code Form is subject to the terms of the Mozilla Public 4 * License, v. 2.0. If a copy of the MPL was not distributed with this 5 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */ 6 7 /* 8 * Implements various macros meant to ease the use of variadic macros. 9 */ 10 11 #ifndef mozilla_MacroArgs_h 12 #define mozilla_MacroArgs_h 13 14 // Concatenates pre-processor tokens in a way that can be used with __LINE__. 15 #define MOZ_CONCAT2(x, y) x##y 16 #define MOZ_CONCAT(x, y) MOZ_CONCAT2(x, y) 17 18 /* 19 * MOZ_ARG_COUNT(...) counts the number of variadic arguments. 20 * You must pass in between 0 and 50 (inclusive) variadic arguments. 21 * For example: 22 * 23 * MOZ_ARG_COUNT() expands to 0 24 * MOZ_ARG_COUNT(a) expands to 1 25 * MOZ_ARG_COUNT(a, b) expands to 2 26 * 27 * Implementation notes: 28 * The `##__VA_ARGS__` form is a GCC extension that removes the comma if 29 * __VA_ARGS__ is empty. It is supported by Clang too. MSVC ignores ##, 30 * and its default behavior is already to strip the comma when __VA_ARGS__ 31 * is empty. 32 * 33 * So MOZ_MACROARGS_ARG_COUNT_HELPER() expands to 34 * (_, 50, 49, ...) 35 * MOZ_MACROARGS_ARG_COUNT_HELPER(a) expands to 36 * (_, a, 50, 49, ...) 37 * etc. 38 */ 39 #define MOZ_ARG_COUNT(...) \ 40 MOZ_MACROARGS_ARG_COUNT_HELPER2(MOZ_MACROARGS_ARG_COUNT_HELPER(__VA_ARGS__)) 41 42 #define MOZ_MACROARGS_ARG_COUNT_HELPER(...) \ 43 (_, ##__VA_ARGS__, 50, 49, 48, 47, 46, 45, 44, 43, 42, 41, 40, 39, 38, 37, \ 44 36, 35, 34, 33, 32, 31, 30, 29, 28, 27, 26, 25, 24, 23, 22, 21, 20, 19, 18, \ 45 17, 16, 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0) 46 47 #define MOZ_MACROARGS_ARG_COUNT_HELPER2(aArgs) \ 48 MOZ_MACROARGS_ARG_COUNT_HELPER3 aArgs 49 50 #define MOZ_MACROARGS_ARG_COUNT_HELPER3( \ 51 a0, a1, a2, a3, a4, a5, a6, a7, a8, a9, a10, a11, a12, a13, a14, a15, a16, \ 52 a17, a18, a19, a20, a21, a22, a23, a24, a25, a26, a27, a28, a29, a30, a31, \ 53 a32, a33, a34, a35, a36, a37, a38, a39, a40, a41, a42, a43, a44, a45, a46, \ 54 a47, a48, a49, a50, a51, ...) \ 55 a51 56 57 /* 58 * MOZ_PASTE_PREFIX_AND_ARG_COUNT(aPrefix, ...) counts the number of variadic 59 * arguments and prefixes it with |aPrefix|. For example: 60 * 61 * MOZ_PASTE_PREFIX_AND_ARG_COUNT(, foo, 42) expands to 2 62 * MOZ_PASTE_PREFIX_AND_ARG_COUNT(A, foo, 42, bar) expands to A3 63 * MOZ_PASTE_PREFIX_AND_ARG_COUNT(A) expands to A0 64 * MOZ_PASTE_PREFIX_AND_ARG_COUNT() expands to 0, but MSVC warns there 65 * aren't enough arguments given. 66 * 67 * You must pass in between 0 and 50 (inclusive) variadic arguments, past 68 * |aPrefix|. 69 */ 70 #define MOZ_PASTE_PREFIX_AND_ARG_COUNT_GLUE(a, b) a b 71 #define MOZ_PASTE_PREFIX_AND_ARG_COUNT(aPrefix, ...) \ 72 MOZ_PASTE_PREFIX_AND_ARG_COUNT_GLUE(MOZ_CONCAT, \ 73 (aPrefix, MOZ_ARG_COUNT(__VA_ARGS__))) 74 75 /* 76 * MOZ_ARGS_AFTER_N expands to its arguments excluding the first |N| 77 * arguments. For example: 78 * 79 * MOZ_ARGS_AFTER_2(a, b, c, d) expands to: c, d 80 */ 81 #define MOZ_ARGS_AFTER_1(a1, ...) __VA_ARGS__ 82 #define MOZ_ARGS_AFTER_2(a1, a2, ...) __VA_ARGS__ 83 84 /* 85 * MOZ_ARG_N expands to its |N|th argument. 86 */ 87 #define MOZ_ARG_1(a1, ...) a1 88 #define MOZ_ARG_2(a1, a2, ...) a2 89 #define MOZ_ARG_3(a1, a2, a3, ...) a3 90 #define MOZ_ARG_4(a1, a2, a3, a4, ...) a4 91 #define MOZ_ARG_5(a1, a2, a3, a4, a5, ...) a5 92 #define MOZ_ARG_6(a1, a2, a3, a4, a5, a6, ...) a6 93 #define MOZ_ARG_7(a1, a2, a3, a4, a5, a6, a7, ...) a7 94 #define MOZ_ARG_8(a1, a2, a3, a4, a5, a6, a7, a8, ...) a8 95 #define MOZ_ARG_9(a1, a2, a3, a4, a5, a6, a7, a8, a9, ...) a9 96 97 #endif /* mozilla_MacroArgs_h */