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Diffstat (limited to 'include/onlineupdate/mozilla/MacroArgs.h')
| -rw-r--r-- | include/onlineupdate/mozilla/MacroArgs.h | 105 |
1 files changed, 105 insertions, 0 deletions
diff --git a/include/onlineupdate/mozilla/MacroArgs.h b/include/onlineupdate/mozilla/MacroArgs.h new file mode 100644 index 000000000..c8b733821 --- /dev/null +++ b/include/onlineupdate/mozilla/MacroArgs.h @@ -0,0 +1,105 @@ +/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */ +/* vim: set ts=8 sts=2 et sw=2 tw=80: */ +/* This Source Code Form is subject to the terms of the Mozilla Public + * License, v. 2.0. If a copy of the MPL was not distributed with this + * file, You can obtain one at http://mozilla.org/MPL/2.0/. */ + +/* + * Implements various macros meant to ease the use of variadic macros. + */ + +#ifndef mozilla_MacroArgs_h +#define mozilla_MacroArgs_h + +/* + * MOZ_PASTE_PREFIX_AND_ARG_COUNT(aPrefix, ...) counts the number of variadic + * arguments and prefixes it with |aPrefix|. For example: + * + * MOZ_PASTE_PREFIX_AND_ARG_COUNT(, foo, 42) expands to 2 + * MOZ_PASTE_PREFIX_AND_ARG_COUNT(A, foo, 42, bar) expands to A3 + * + * You must pass in between 1 and 50 (inclusive) variadic arguments, past + * |aPrefix|. It is not legal to do + * + * MOZ_PASTE_PREFIX_AND_ARG_COUNT(prefix) + * + * (that is, pass in 0 variadic arguments). To ensure that a compile-time + * error occurs when these constraints are violated, use the + * MOZ_STATIC_ASSERT_VALID_ARG_COUNT macro with the same variaidc arguments + * wherever this macro is used. + * + * Passing (__VA_ARGS__, <rest of arguments>) rather than simply calling + * MOZ_MACROARGS_ARG_COUNT_HELPER2(__VA_ARGS__, <rest of arguments>) very + * carefully tiptoes around a MSVC bug where it improperly expands __VA_ARGS__ + * as a single token in argument lists. For details, see: + * + * http://connect.microsoft.com/VisualStudio/feedback/details/380090/variadic-macro-replacement + * http://cplusplus.co.il/2010/07/17/variadic-macro-to-count-number-of-arguments/#comment-644 + */ +#define MOZ_PASTE_PREFIX_AND_ARG_COUNT(aPrefix, ...) \ + MOZ_MACROARGS_ARG_COUNT_HELPER((__VA_ARGS__, \ + aPrefix##50, aPrefix##49, aPrefix##48, aPrefix##47, aPrefix##46, \ + aPrefix##45, aPrefix##44, aPrefix##43, aPrefix##42, aPrefix##41, \ + aPrefix##40, aPrefix##39, aPrefix##38, aPrefix##37, aPrefix##36, \ + aPrefix##35, aPrefix##34, aPrefix##33, aPrefix##32, aPrefix##31, \ + aPrefix##30, aPrefix##29, aPrefix##28, aPrefix##27, aPrefix##26, \ + aPrefix##25, aPrefix##24, aPrefix##23, aPrefix##22, aPrefix##21, \ + aPrefix##20, aPrefix##19, aPrefix##18, aPrefix##17, aPrefix##16, \ + aPrefix##15, aPrefix##14, aPrefix##13, aPrefix##12, aPrefix##11, \ + aPrefix##10, aPrefix##9, aPrefix##8, aPrefix##7, aPrefix##6, \ + aPrefix##5, aPrefix##4, aPrefix##3, aPrefix##2, aPrefix##1, aPrefix##0)) + +#define MOZ_MACROARGS_ARG_COUNT_HELPER(aArgs) \ + MOZ_MACROARGS_ARG_COUNT_HELPER2 aArgs + +#define MOZ_MACROARGS_ARG_COUNT_HELPER2( \ + a1, a2, a3, a4, a5, a6, a7, a8, a9, a10, \ + a11, a12, a13, a14, a15, a16, a17, a18, a19, a20, \ + a21, a22, a23, a24, a25, a26, a27, a28, a29, a30, \ + a31, a32, a33, a34, a35, a36, a37, a38, a39, a40, \ + a41, a42, a43, a44, a45, a46, a47, a48, a49, a50, \ + a51, ...) a51 + +/* + * MOZ_STATIC_ASSERT_VALID_ARG_COUNT ensures that a compile-time error occurs + * when the argument count constraints of MOZ_PASTE_PREFIX_AND_ARG_COUNT are + * violated. Use this macro wherever MOZ_PASTE_PREFIX_AND_ARG_COUNT is used + * and pass it the same variadic arguments. + * + * This macro employs a few dirty tricks to function. To detect the zero + * argument case, |(__VA_ARGS__)| is stringified, sizeof-ed, and compared to + * what it should be in the absence of arguments. + * + * Detecting too many arguments is a little trickier. With a valid argument + * count and a prefix of 1, MOZ_PASTE_PREFIX_AND_ARG_COUNT expands to e.g. 14. + * With a prefix of 0.0, it expands to e.g. 0.04. If there are too many + * arguments, it expands to the first argument over the limit. If this + * exceeding argument is a number, the assertion will fail as there is no + * number than can simultaneously be both > 10 and == 0. If the exceeding + * argument is not a number, a compile-time error should still occur due to + * the operations performed on it. + */ +#define MOZ_MACROARGS_STRINGIFY_HELPER(x) #x +#define MOZ_STATIC_ASSERT_VALID_ARG_COUNT(...) \ + static_assert( \ + sizeof(MOZ_MACROARGS_STRINGIFY_HELPER((__VA_ARGS__))) != sizeof("()") && \ + (MOZ_PASTE_PREFIX_AND_ARG_COUNT(1, __VA_ARGS__)) > 10 && \ + (int)(MOZ_PASTE_PREFIX_AND_ARG_COUNT(0.0, __VA_ARGS__)) == 0, \ + "MOZ_STATIC_ASSERT_VALID_ARG_COUNT requires 1 to 50 arguments") /* ; */ + +/* + * MOZ_ARGS_AFTER_N expands to its arguments excluding the first |N| + * arguments. For example: + * + * MOZ_ARGS_AFTER_2(a, b, c, d) expands to: c, d + */ +#define MOZ_ARGS_AFTER_1(a1, ...) __VA_ARGS__ +#define MOZ_ARGS_AFTER_2(a1, a2, ...) __VA_ARGS__ + +/* + * MOZ_ARG_N expands to its |N|th argument. + */ +#define MOZ_ARG_1(a1, ...) a1 +#define MOZ_ARG_2(a1, a2, ...) a2 + +#endif /* mozilla_MacroArgs_h */ |