Backed out 7 changesets (bug 1839993) for causing build bustages on DecoderTemplate...
[gecko.git] / mfbt / MacroArgs.h
blob9afaaef945a54739fa34a1cd7714e2fdeb47b897
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/. */
7 /*
8 * Implements various macros meant to ease the use of variadic macros.
9 */
11 #ifndef mozilla_MacroArgs_h
12 #define mozilla_MacroArgs_h
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)
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:
23 * MOZ_ARG_COUNT() expands to 0
24 * MOZ_ARG_COUNT(a) expands to 1
25 * MOZ_ARG_COUNT(a, b) expands to 2
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.
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.
39 #define MOZ_ARG_COUNT(...) \
40 MOZ_MACROARGS_ARG_COUNT_HELPER2(MOZ_MACROARGS_ARG_COUNT_HELPER(__VA_ARGS__))
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)
47 #define MOZ_MACROARGS_ARG_COUNT_HELPER2(aArgs) \
48 MOZ_MACROARGS_ARG_COUNT_HELPER3 aArgs
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
58 * MOZ_PASTE_PREFIX_AND_ARG_COUNT(aPrefix, ...) counts the number of variadic
59 * arguments and prefixes it with |aPrefix|. For example:
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.
67 * You must pass in between 0 and 50 (inclusive) variadic arguments, past
68 * |aPrefix|.
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__)))
76 * MOZ_ARGS_AFTER_N expands to its arguments excluding the first |N|
77 * arguments. For example:
79 * MOZ_ARGS_AFTER_2(a, b, c, d) expands to: c, d
81 #define MOZ_ARGS_AFTER_1(a1, ...) __VA_ARGS__
82 #define MOZ_ARGS_AFTER_2(a1, a2, ...) __VA_ARGS__
85 * MOZ_ARG_N expands to its |N|th argument.
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
97 #endif /* mozilla_MacroArgs_h */