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99 lines
2.8 KiB
C
99 lines
2.8 KiB
C
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/*
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* Copyright 2016 Facebook, Inc.
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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// @author: Andrei Alexandrescu
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#pragma once
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/**
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* Necessarily evil preprocessor-related amenities.
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*/
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// MSVC's preprocessor is a pain, so we have to
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// forcefully expand the VA args in some places.
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#define FB_VA_GLUE(a, b) a b
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/**
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* FB_ONE_OR_NONE(hello, world) expands to hello and
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* FB_ONE_OR_NONE(hello) expands to nothing. This macro is used to
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* insert or eliminate text based on the presence of another argument.
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*/
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#define FB_ONE_OR_NONE(a, ...) FB_VA_GLUE(FB_THIRD, (a, ## __VA_ARGS__, a))
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#define FB_THIRD(a, b, ...) __VA_ARGS__
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/**
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* Helper macro that extracts the first argument out of a list of any
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* number of arguments.
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*/
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#define FB_ARG_1(a, ...) a
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/**
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* Helper macro that extracts the second argument out of a list of any
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* number of arguments. If only one argument is given, it returns
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* that.
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*/
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#ifdef _MSC_VER
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// GCC refuses to expand this correctly if this macro itself was
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// called with FB_VA_GLUE :(
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#define FB_ARG_2_OR_1(...) \
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FB_VA_GLUE(FB_ARG_2_OR_1_IMPL, (__VA_ARGS__, __VA_ARGS__))
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#else
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#define FB_ARG_2_OR_1(...) FB_ARG_2_OR_1_IMPL(__VA_ARGS__, __VA_ARGS__)
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#endif
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// Support macro for the above
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#define FB_ARG_2_OR_1_IMPL(a, b, ...) b
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/**
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* Helper macro that provides a way to pass argument with commas in it to
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* some other macro whose syntax doesn't allow using extra parentheses.
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* Example:
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*
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* #define MACRO(type, name) type name
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* MACRO(FB_SINGLE_ARG(std::pair<size_t, size_t>), x);
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*
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*/
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#define FB_SINGLE_ARG(...) __VA_ARGS__
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/**
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* Helper macro that just ignores its parameters.
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*/
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#define FOLLY_IGNORE(...)
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/**
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* Helper macro that just ignores its parameters and inserts a semicolon.
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*/
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#define FOLLY_SEMICOLON(...) ;
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/**
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* FB_ANONYMOUS_VARIABLE(str) introduces an identifier starting with
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* str and ending with a number that varies with the line.
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*/
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#ifndef FB_ANONYMOUS_VARIABLE
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#define FB_CONCATENATE_IMPL(s1, s2) s1##s2
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#define FB_CONCATENATE(s1, s2) FB_CONCATENATE_IMPL(s1, s2)
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#ifdef __COUNTER__
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#define FB_ANONYMOUS_VARIABLE(str) FB_CONCATENATE(str, __COUNTER__)
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#else
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#define FB_ANONYMOUS_VARIABLE(str) FB_CONCATENATE(str, __LINE__)
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#endif
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#endif
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/**
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* Use FB_STRINGIZE(x) when you'd want to do what #x does inside
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* another macro expansion.
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*/
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#define FB_STRINGIZE(x) #x
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