如何使用 boost::preprocessor 解压缩序列？答案

【问题标题】：How to use boost::preprocessor to unzip a sequence?如何使用 boost::preprocessor 解压缩序列？
【发布时间】：2014-12-16 00:20:18
【问题描述】：

如何使用 boost::preprocessor 解压一系列pair？

例如，我有一个如下的序列（逗号之间没有关系）

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

想要转换成

int,double,float

和

x,y,z

通过使用 macor like

UNZIP(i, seq)

其中i 是索引。

【问题讨论】：

最后两个元素之间有逗号，前两个元素之间没有逗号。你喜欢哪个？实际上，用逗号看起来好多了。

标签： c++ boost boost-preprocessor

【解决方案1】：

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

LIVE DEMO

#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

【讨论】：

【解决方案2】：

假设您的意思是逗号 ((int,x),(double,y),(float,z))，Boost.PP 效果很好：

#include <boost/preprocessor.hpp> //or smaller individual headers

//SEQ_ENUM adds commas between each element of the sequence
//the sequence is transformed from what's passed into the ...
//the invocation of UNZIP_MACRO is given the index to use in each element as data
#define UNZIP(i, ...)                             \
    BOOST_PP_SEQ_ENUM(                            \
        BOOST_PP_SEQ_TRANSFORM(                   \
            UNZIP_MACRO,                          \
            i,                                    \
            BOOST_PP_VARIADIC_TO_SEQ(__VA_ARGS__) \
        )                                         \
    )

//called with each element of the sequence
#define UNZIP_MACRO(s, data, elem) \
    BOOST_PP_TUPLE_ELEM(data, elem)


#define ZIPPED_SEQUENCE (int,x),(double,y),(float,z)

UNZIP(0, ZIPPED_SEQUENCE) //int, double, float
UNZIP(1, ZIPPED_SEQUENCE) //x, y, z

【讨论】：