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rocksdb/thrift/folly/Preprocessor.h

71 lines
2.0 KiB

/*
* Copyright 2012 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
#ifndef FOLLY_PREPROCESSOR_
#define FOLLY_PREPROCESSOR_
/**
* Necessarily evil preprocessor-related amenities.
*/
/**
* 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_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.
*/
#define FB_ARG_2_OR_1(...) FB_ARG_2_OR_1_IMPL(__VA_ARGS__, __VA_ARGS__)
// Support macro for the above
#define FB_ARG_2_OR_1_IMPL(a, b, ...) b
/**
* 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(name) when you'd want to do what #name does inside
* another macro expansion.
*/
#define FB_STRINGIZE(name) #name
#endif // FOLLY_PREPROCESSOR_