| /* |
| * Copyright 2017 Facebook, Inc. |
| * |
| * Licensed under the Apache License, Version 2.0 (the "License"); |
| * you may not use this file except in compliance with the License. |
| * You may obtain a copy of the License at |
| * |
| * http://www.apache.org/licenses/LICENSE-2.0 |
| * |
| * Unless required by applicable law or agreed to in writing, software |
| * distributed under the License is distributed on an "AS IS" BASIS, |
| * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| * See the License for the specific language governing permissions and |
| * limitations under the License. |
| */ |
| |
| // @author: Andrei Alexandrescu |
| |
| #pragma once |
| |
| /** |
| * Necessarily evil preprocessor-related amenities. |
| */ |
| |
| // MSVC's preprocessor is a pain, so we have to |
| // forcefully expand the VA args in some places. |
| #define FB_VA_GLUE(a, b) a b |
| |
| /** |
| * FB_ONE_OR_NONE(hello, world) expands to hello and |
| * FB_ONE_OR_NONE(hello) expands to nothing. This macro is used to |
| * insert or eliminate text based on the presence of another argument. |
| */ |
| #define FB_ONE_OR_NONE(a, ...) FB_VA_GLUE(FB_THIRD, (a, ## __VA_ARGS__, a)) |
| #define FB_THIRD(a, b, ...) __VA_ARGS__ |
| |
| /** |
| * Helper macro that extracts the first argument out of a list of any |
| * number of arguments. |
| */ |
| #define FB_ARG_1(a, ...) a |
| |
| /** |
| * Helper macro that extracts the second argument out of a list of any |
| * number of arguments. If only one argument is given, it returns |
| * that. |
| */ |
| #ifdef _MSC_VER |
| // GCC refuses to expand this correctly if this macro itself was |
| // called with FB_VA_GLUE :( |
| #define FB_ARG_2_OR_1(...) \ |
| FB_VA_GLUE(FB_ARG_2_OR_1_IMPL, (__VA_ARGS__, __VA_ARGS__)) |
| #else |
| #define FB_ARG_2_OR_1(...) FB_ARG_2_OR_1_IMPL(__VA_ARGS__, __VA_ARGS__) |
| #endif |
| // Support macro for the above |
| #define FB_ARG_2_OR_1_IMPL(a, b, ...) b |
| |
| /** |
| * Helper macro that provides a way to pass argument with commas in it to |
| * some other macro whose syntax doesn't allow using extra parentheses. |
| * Example: |
| * |
| * #define MACRO(type, name) type name |
| * MACRO(FB_SINGLE_ARG(std::pair<size_t, size_t>), x); |
| * |
| */ |
| #define FB_SINGLE_ARG(...) __VA_ARGS__ |
| |
| /** |
| * Helper macro that just ignores its parameters. |
| */ |
| #define FOLLY_IGNORE(...) |
| |
| /** |
| * Helper macro that just ignores its parameters and inserts a semicolon. |
| */ |
| #define FOLLY_SEMICOLON(...) ; |
| |
| /** |
| * FB_ANONYMOUS_VARIABLE(str) introduces an identifier starting with |
| * str and ending with a number that varies with the line. |
| */ |
| #ifndef FB_ANONYMOUS_VARIABLE |
| #define FB_CONCATENATE_IMPL(s1, s2) s1##s2 |
| #define FB_CONCATENATE(s1, s2) FB_CONCATENATE_IMPL(s1, s2) |
| #ifdef __COUNTER__ |
| #define FB_ANONYMOUS_VARIABLE(str) FB_CONCATENATE(str, __COUNTER__) |
| #else |
| #define FB_ANONYMOUS_VARIABLE(str) FB_CONCATENATE(str, __LINE__) |
| #endif |
| #endif |
| |
| /** |
| * Use FB_STRINGIZE(x) when you'd want to do what #x does inside |
| * another macro expansion. |
| */ |
| #define FB_STRINGIZE(x) #x |