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comparison: mfbt/MacroArgs.h
mfbt/MacroArgs.h
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- changeset 8
- 97036ab72558
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| -1:000000000000 | 0:c115905c01d1 |
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| 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 /* | |
| 15 * MOZ_PASTE_PREFIX_AND_ARG_COUNT(aPrefix, ...) counts the number of variadic | |
| 16 * arguments and prefixes it with |aPrefix|. For example: | |
| 17 * | |
| 18 * MOZ_PASTE_PREFIX_AND_ARG_COUNT(, foo, 42) expands to 2 | |
| 19 * MOZ_PASTE_PREFIX_AND_ARG_COUNT(A, foo, 42, bar) expands to A3 | |
| 20 * | |
| 21 * You must pass in between 1 and 50 (inclusive) variadic arguments, past | |
| 22 * |aPrefix|. It is not legal to do | |
| 23 * | |
| 24 * MOZ_PASTE_PREFIX_AND_ARG_COUNT(prefix) | |
| 25 * | |
| 26 * (that is, pass in 0 variadic arguments). To ensure that a compile-time | |
| 27 * error occurs when these constraints are violated, use the | |
| 28 * MOZ_STATIC_ASSERT_VALID_ARG_COUNT macro with the same variaidc arguments | |
| 29 * wherever this macro is used. | |
| 30 * | |
| 31 * Passing (__VA_ARGS__, <rest of arguments>) rather than simply calling | |
| 32 * MOZ_MACROARGS_ARG_COUNT_HELPER2(__VA_ARGS__, <rest of arguments>) very | |
| 33 * carefully tiptoes around a MSVC bug where it improperly expands __VA_ARGS__ | |
| 34 * as a single token in argument lists. For details, see: | |
| 35 * | |
| 36 * http://connect.microsoft.com/VisualStudio/feedback/details/380090/variadic-macro-replacement | |
| 37 * http://cplusplus.co.il/2010/07/17/variadic-macro-to-count-number-of-arguments/#comment-644 | |
| 38 */ | |
| 39 #define MOZ_PASTE_PREFIX_AND_ARG_COUNT(aPrefix, ...) \ | |
| 40 MOZ_MACROARGS_ARG_COUNT_HELPER((__VA_ARGS__, \ | |
| 41 aPrefix##50, aPrefix##49, aPrefix##48, aPrefix##47, aPrefix##46, \ | |
| 42 aPrefix##45, aPrefix##44, aPrefix##43, aPrefix##42, aPrefix##41, \ | |
| 43 aPrefix##40, aPrefix##39, aPrefix##38, aPrefix##37, aPrefix##36, \ | |
| 44 aPrefix##35, aPrefix##34, aPrefix##33, aPrefix##32, aPrefix##31, \ | |
| 45 aPrefix##30, aPrefix##29, aPrefix##28, aPrefix##27, aPrefix##26, \ | |
| 46 aPrefix##25, aPrefix##24, aPrefix##23, aPrefix##22, aPrefix##21, \ | |
| 47 aPrefix##20, aPrefix##19, aPrefix##18, aPrefix##17, aPrefix##16, \ | |
| 48 aPrefix##15, aPrefix##14, aPrefix##13, aPrefix##12, aPrefix##11, \ | |
| 49 aPrefix##10, aPrefix##9, aPrefix##8, aPrefix##7, aPrefix##6, \ | |
| 50 aPrefix##5, aPrefix##4, aPrefix##3, aPrefix##2, aPrefix##1, aPrefix##0)) | |
| 51 | |
| 52 #define MOZ_MACROARGS_ARG_COUNT_HELPER(aArgs) \ | |
| 53 MOZ_MACROARGS_ARG_COUNT_HELPER2 aArgs | |
| 54 | |
| 55 #define MOZ_MACROARGS_ARG_COUNT_HELPER2( \ | |
| 56 a1, a2, a3, a4, a5, a6, a7, a8, a9, a10, \ | |
| 57 a11, a12, a13, a14, a15, a16, a17, a18, a19, a20, \ | |
| 58 a21, a22, a23, a24, a25, a26, a27, a28, a29, a30, \ | |
| 59 a31, a32, a33, a34, a35, a36, a37, a38, a39, a40, \ | |
| 60 a41, a42, a43, a44, a45, a46, a47, a48, a49, a50, \ | |
| 61 a51, ...) a51 | |
| 62 | |
| 63 /* | |
| 64 * MOZ_STATIC_ASSERT_VALID_ARG_COUNT ensures that a compile-time error occurs | |
| 65 * when the argument count constraints of MOZ_PASTE_PREFIX_AND_ARG_COUNT are | |
| 66 * violated. Use this macro wherever MOZ_PASTE_PREFIX_AND_ARG_COUNT is used | |
| 67 * and pass it the same variadic arguments. | |
| 68 * | |
| 69 * This macro employs a few dirty tricks to function. To detect the zero | |
| 70 * argument case, |(__VA_ARGS__)| is stringified, sizeof-ed, and compared to | |
| 71 * what it should be in the absence of arguments. | |
| 72 * | |
| 73 * Detecting too many arguments is a little trickier. With a valid argument | |
| 74 * count and a prefix of 1, MOZ_PASTE_PREFIX_AND_ARG_COUNT expands to e.g. 14. | |
| 75 * With a prefix of 0.0, it expands to e.g. 0.04. If there are too many | |
| 76 * arguments, it expands to the first argument over the limit. If this | |
| 77 * exceeding argument is a number, the assertion will fail as there is no | |
| 78 * number than can simultaneously be both > 10 and < 0.1. If the exceeding | |
| 79 * argument is not a number, a compile-time error will still occur because the | |
| 80 * exceeding argument is compared to an int and a double. | |
| 81 */ | |
| 82 #define MOZ_MACROARGS_STRINGIFY_HELPER(x) #x | |
| 83 #define MOZ_STATIC_ASSERT_VALID_ARG_COUNT(...) \ | |
| 84 static_assert( \ | |
| 85 sizeof(MOZ_MACROARGS_STRINGIFY_HELPER((__VA_ARGS__))) != sizeof("()") && \ | |
| 86 (MOZ_PASTE_PREFIX_AND_ARG_COUNT(1, __VA_ARGS__)) > 10 && \ | |
| 87 (MOZ_PASTE_PREFIX_AND_ARG_COUNT(0.0, __VA_ARGS__)) < 0.1, \ | |
| 88 "MOZ_STATIC_ASSERT_VALID_ARG_COUNT requires 1 to 50 arguments") /* ; */ | |
| 89 | |
| 90 /* | |
| 91 * MOZ_ARGS_AFTER_N expands to its arguments excluding the first |N| | |
| 92 * arguments. For example: | |
| 93 * | |
| 94 * MOZ_ARGS_AFTER_2(a, b, c, d) expands to: c, d | |
| 95 */ | |
| 96 #define MOZ_ARGS_AFTER_1(a1, ...) __VA_ARGS__ | |
| 97 #define MOZ_ARGS_AFTER_2(a1, a2, ...) __VA_ARGS__ | |
| 98 | |
| 99 /* | |
| 100 * MOZ_ARG_N expands to its |N|th argument. | |
| 101 */ | |
| 102 #define MOZ_ARG_1(a1, ...) a1 | |
| 103 #define MOZ_ARG_2(a1, a2, ...) a2 | |
| 104 | |
| 105 #endif /* mozilla_MacroArgs_h */ |
