如何使用boost::预处理器来解压缩序列

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

本文关键字：解压缩 预处理 何使用 boost 处理器      更新时间：2023-10-16

如何使用boost:：预处理器来解压缩对序列？

例如，我有一个序列如下（逗号之间无关紧要）

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

并希望转换为

int,double,float

和

x,y,z

通过使用类似macor的

UNZIP(i, seq)

其中CCD_ 1是索引。

(int, x, 10)(double, y, 20)(float, z, 30)的解压缩，即元素之间不带逗号的序列。

现场演示

#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

假设你指的是逗号（(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
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