如何使用boost :: preprocessor解压缩序列?

问题描述

如何使用boost :: preprocessor解压缩序列对?

How to use boost::preprocessor to unzip a sequence of pairs?

例如，我有一个如下序列(两者之间的逗号无关紧要)

For example, I have a sequence as below (comma between doesn't matter)

(int,x)(double,y)(float,z) or
(int,x),(double,y),(float,z) or
((int)(x))((double)(y))((float)(z))

并想要转换为

int,double,float

和

x,y,z

通过使用macor之类的

By using macor like

UNZIP(i, seq)

其中i是索引.

推荐答案

(int, x, 10)(double, y, 20)(float, z, 30)的解压缩，即元素之间没有逗号的序列.

Unzipping of (int, x, 10)(double, y, 20)(float, z, 30), i.e. sequence without commas between elements.

实时演示

#include <boost/preprocessor/punctuation/comma_if.hpp>
#include <boost/preprocessor/seq/for_each_i.hpp>
#include <boost/preprocessor/seq/pop_front.hpp>
#include <boost/preprocessor/seq/for_each.hpp>
#include <boost/preprocessor/variadic/elem.hpp>
#include <boost/preprocessor/cat.hpp>

// Such technique is used at:
//   http://www.boost.org/doc/libs/1_56_0/boost/fusion/adapted/struct/define_struct.hpp
#define AUXILIARY_0(...) ((__VA_ARGS__)) AUXILIARY_1
#define AUXILIARY_1(...) ((__VA_ARGS__)) AUXILIARY_0
#define AUXILIARY_0_END
#define AUXILIARY_1_END

#define REMOVE_PARENTHESES(...) __VA_ARGS__

#define COMMA_SEPARATED(r, data, i, elem) \
    BOOST_PP_COMMA_IF(i) BOOST_PP_VARIADIC_ELEM(data, REMOVE_PARENTHESES elem) \
/**/

#define ZIPPED_TO_SEQ(zipped) \
    BOOST_PP_SEQ_POP_FRONT(BOOST_PP_CAT(AUXILIARY_0(0)zipped,_END)) \
/**/

#define FOR_EACH_ZIPPED_I(macro, data, zipped) \
    BOOST_PP_SEQ_FOR_EACH_I(macro, data, ZIPPED_TO_SEQ(zipped)) \
/**/

#define UNZIP(i, zipped) FOR_EACH_ZIPPED_I(COMMA_SEPARATED, i, zipped)

/*******************************************************************/
// DEMO:

#define zipped (int, x, 10)(double, y, 20)(float, z, 30)

FIRST:  UNZIP(0, zipped)
SECOND: UNZIP(1, zipped)
THIRD:  UNZIP(2, zipped)

预处理器输出:

FIRST: int , double , float
SECOND: x , y , z
THIRD: 10 , 20 , 30

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