mfbt/MacroArgs.h@6474c204b198 (annotated)
mfbt/MacroArgs.h
Wed, 31 Dec 2014 06:09:35 +0100
- author
- Michael Schloh von Bennewitz <michael@schloh.com>
- date
- Wed, 31 Dec 2014 06:09:35 +0100
- changeset 0
- 6474c204b198
- permissions
- -rw-r--r--
Cloned upstream origin tor-browser at tor-browser-31.3.0esr-4.5-1-build1
revision ID fc1c9ff7c1b2defdbc039f12214767608f46423f for hacking purpose.
| michael@0 | 1 | /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */ |
| michael@0 | 2 | /* vim: set ts=8 sts=2 et sw=2 tw=80: */ |
| michael@0 | 3 | /* This Source Code Form is subject to the terms of the Mozilla Public |
| michael@0 | 4 | * License, v. 2.0. If a copy of the MPL was not distributed with this |
| michael@0 | 5 | * file, You can obtain one at http://mozilla.org/MPL/2.0/. */ |
| michael@0 | 6 | |
| michael@0 | 7 | /* |
| michael@0 | 8 | * Implements various macros meant to ease the use of variadic macros. |
| michael@0 | 9 | */ |
| michael@0 | 10 | |
| michael@0 | 11 | #ifndef mozilla_MacroArgs_h |
| michael@0 | 12 | #define mozilla_MacroArgs_h |
| michael@0 | 13 | |
| michael@0 | 14 | /* |
| michael@0 | 15 | * MOZ_PASTE_PREFIX_AND_ARG_COUNT(aPrefix, ...) counts the number of variadic |
| michael@0 | 16 | * arguments and prefixes it with |aPrefix|. For example: |
| michael@0 | 17 | * |
| michael@0 | 18 | * MOZ_PASTE_PREFIX_AND_ARG_COUNT(, foo, 42) expands to 2 |
| michael@0 | 19 | * MOZ_PASTE_PREFIX_AND_ARG_COUNT(A, foo, 42, bar) expands to A3 |
| michael@0 | 20 | * |
| michael@0 | 21 | * You must pass in between 1 and 50 (inclusive) variadic arguments, past |
| michael@0 | 22 | * |aPrefix|. It is not legal to do |
| michael@0 | 23 | * |
| michael@0 | 24 | * MOZ_PASTE_PREFIX_AND_ARG_COUNT(prefix) |
| michael@0 | 25 | * |
| michael@0 | 26 | * (that is, pass in 0 variadic arguments). To ensure that a compile-time |
| michael@0 | 27 | * error occurs when these constraints are violated, use the |
| michael@0 | 28 | * MOZ_STATIC_ASSERT_VALID_ARG_COUNT macro with the same variaidc arguments |
| michael@0 | 29 | * wherever this macro is used. |
| michael@0 | 30 | * |
| michael@0 | 31 | * Passing (__VA_ARGS__, <rest of arguments>) rather than simply calling |
| michael@0 | 32 | * MOZ_MACROARGS_ARG_COUNT_HELPER2(__VA_ARGS__, <rest of arguments>) very |
| michael@0 | 33 | * carefully tiptoes around a MSVC bug where it improperly expands __VA_ARGS__ |
| michael@0 | 34 | * as a single token in argument lists. For details, see: |
| michael@0 | 35 | * |
| michael@0 | 36 | * http://connect.microsoft.com/VisualStudio/feedback/details/380090/variadic-macro-replacement |
| michael@0 | 37 | * http://cplusplus.co.il/2010/07/17/variadic-macro-to-count-number-of-arguments/#comment-644 |
| michael@0 | 38 | */ |
| michael@0 | 39 | #define MOZ_PASTE_PREFIX_AND_ARG_COUNT(aPrefix, ...) \ |
| michael@0 | 40 | MOZ_MACROARGS_ARG_COUNT_HELPER((__VA_ARGS__, \ |
| michael@0 | 41 | aPrefix##50, aPrefix##49, aPrefix##48, aPrefix##47, aPrefix##46, \ |
| michael@0 | 42 | aPrefix##45, aPrefix##44, aPrefix##43, aPrefix##42, aPrefix##41, \ |
| michael@0 | 43 | aPrefix##40, aPrefix##39, aPrefix##38, aPrefix##37, aPrefix##36, \ |
| michael@0 | 44 | aPrefix##35, aPrefix##34, aPrefix##33, aPrefix##32, aPrefix##31, \ |
| michael@0 | 45 | aPrefix##30, aPrefix##29, aPrefix##28, aPrefix##27, aPrefix##26, \ |
| michael@0 | 46 | aPrefix##25, aPrefix##24, aPrefix##23, aPrefix##22, aPrefix##21, \ |
| michael@0 | 47 | aPrefix##20, aPrefix##19, aPrefix##18, aPrefix##17, aPrefix##16, \ |
| michael@0 | 48 | aPrefix##15, aPrefix##14, aPrefix##13, aPrefix##12, aPrefix##11, \ |
| michael@0 | 49 | aPrefix##10, aPrefix##9, aPrefix##8, aPrefix##7, aPrefix##6, \ |
| michael@0 | 50 | aPrefix##5, aPrefix##4, aPrefix##3, aPrefix##2, aPrefix##1, aPrefix##0)) |
| michael@0 | 51 | |
| michael@0 | 52 | #define MOZ_MACROARGS_ARG_COUNT_HELPER(aArgs) \ |
| michael@0 | 53 | MOZ_MACROARGS_ARG_COUNT_HELPER2 aArgs |
| michael@0 | 54 | |
| michael@0 | 55 | #define MOZ_MACROARGS_ARG_COUNT_HELPER2( \ |
| michael@0 | 56 | a1, a2, a3, a4, a5, a6, a7, a8, a9, a10, \ |
| michael@0 | 57 | a11, a12, a13, a14, a15, a16, a17, a18, a19, a20, \ |
| michael@0 | 58 | a21, a22, a23, a24, a25, a26, a27, a28, a29, a30, \ |
| michael@0 | 59 | a31, a32, a33, a34, a35, a36, a37, a38, a39, a40, \ |
| michael@0 | 60 | a41, a42, a43, a44, a45, a46, a47, a48, a49, a50, \ |
| michael@0 | 61 | a51, ...) a51 |
| michael@0 | 62 | |
| michael@0 | 63 | /* |
| michael@0 | 64 | * MOZ_STATIC_ASSERT_VALID_ARG_COUNT ensures that a compile-time error occurs |
| michael@0 | 65 | * when the argument count constraints of MOZ_PASTE_PREFIX_AND_ARG_COUNT are |
| michael@0 | 66 | * violated. Use this macro wherever MOZ_PASTE_PREFIX_AND_ARG_COUNT is used |
| michael@0 | 67 | * and pass it the same variadic arguments. |
| michael@0 | 68 | * |
| michael@0 | 69 | * This macro employs a few dirty tricks to function. To detect the zero |
| michael@0 | 70 | * argument case, |(__VA_ARGS__)| is stringified, sizeof-ed, and compared to |
| michael@0 | 71 | * what it should be in the absence of arguments. |
| michael@0 | 72 | * |
| michael@0 | 73 | * Detecting too many arguments is a little trickier. With a valid argument |
| michael@0 | 74 | * count and a prefix of 1, MOZ_PASTE_PREFIX_AND_ARG_COUNT expands to e.g. 14. |
| michael@0 | 75 | * With a prefix of 0.0, it expands to e.g. 0.04. If there are too many |
| michael@0 | 76 | * arguments, it expands to the first argument over the limit. If this |
| michael@0 | 77 | * exceeding argument is a number, the assertion will fail as there is no |
| michael@0 | 78 | * number than can simultaneously be both > 10 and < 0.1. If the exceeding |
| michael@0 | 79 | * argument is not a number, a compile-time error will still occur because the |
| michael@0 | 80 | * exceeding argument is compared to an int and a double. |
| michael@0 | 81 | */ |
| michael@0 | 82 | #define MOZ_MACROARGS_STRINGIFY_HELPER(x) #x |
| michael@0 | 83 | #define MOZ_STATIC_ASSERT_VALID_ARG_COUNT(...) \ |
| michael@0 | 84 | static_assert( \ |
| michael@0 | 85 | sizeof(MOZ_MACROARGS_STRINGIFY_HELPER((__VA_ARGS__))) != sizeof("()") && \ |
| michael@0 | 86 | (MOZ_PASTE_PREFIX_AND_ARG_COUNT(1, __VA_ARGS__)) > 10 && \ |
| michael@0 | 87 | (MOZ_PASTE_PREFIX_AND_ARG_COUNT(0.0, __VA_ARGS__)) < 0.1, \ |
| michael@0 | 88 | "MOZ_STATIC_ASSERT_VALID_ARG_COUNT requires 1 to 50 arguments") /* ; */ |
| michael@0 | 89 | |
| michael@0 | 90 | /* |
| michael@0 | 91 | * MOZ_ARGS_AFTER_N expands to its arguments excluding the first |N| |
| michael@0 | 92 | * arguments. For example: |
| michael@0 | 93 | * |
| michael@0 | 94 | * MOZ_ARGS_AFTER_2(a, b, c, d) expands to: c, d |
| michael@0 | 95 | */ |
| michael@0 | 96 | #define MOZ_ARGS_AFTER_1(a1, ...) __VA_ARGS__ |
| michael@0 | 97 | #define MOZ_ARGS_AFTER_2(a1, a2, ...) __VA_ARGS__ |
| michael@0 | 98 | |
| michael@0 | 99 | /* |
| michael@0 | 100 | * MOZ_ARG_N expands to its |N|th argument. |
| michael@0 | 101 | */ |
| michael@0 | 102 | #define MOZ_ARG_1(a1, ...) a1 |
| michael@0 | 103 | #define MOZ_ARG_2(a1, a2, ...) a2 |
| michael@0 | 104 | |
| michael@0 | 105 | #endif /* mozilla_MacroArgs_h */ |
