c++ - BOOST_PP_REPEAT 与 boost::fusion::size

Question

我想在编译时迭代结构并写入输出迭代次数。只是提一下 - 在实际情况下，我会在数据中传递更多参数。

#include <iostream>
#include <string>
#include <vector>
#include <boost/fusion/include/adapt_struct.hpp>
#include <boost/fusion/include/size.hpp>
#include <boost/preprocessor/repetition/repeat.hpp>

struct MyStruct
{
    int x;
    int y;
};

BOOST_FUSION_ADAPT_STRUCT(
    MyStruct,
    (int, x)
    (int, y)    
    )

#define PRINT(unused, number, data) \
    std::cout << number << std::endl;

int main()
{
    MyStruct s;

    std::cout << boost::fusion::size(s) << std::endl;
    //line below works - it iterate and write output
    BOOST_PP_REPEAT(2, PRINT, "here I will pass my data")

    //this won't compile 
    //BOOST_PP_REPEAT(boost::fusion::size(s), PRINT, "here i will pass my data")
}

如何修复有问题的行，以便在我向结构中添加更多成员时它能正常工作？我需要 C++03 的解决方案:(

Answer 1

您可以使用遍历每个元素的 boost::fusion::for_each 而不是使用 BOOST_PP_REPEAT。示例:

#include <iostream>
#include <string>
#include <vector>
#include <boost/fusion/include/adapt_struct.hpp>
#include <boost/fusion/include/size.hpp>
#include <boost/preprocessor/repetition/repeat.hpp>
#include <boost/fusion/algorithm/iteration/for_each.hpp>

struct MyStruct {
    int x;
    int y;
};

BOOST_FUSION_ADAPT_STRUCT(
    MyStruct,
    (int, x)
    (int, y)
)

template<typename Data>
struct PrintWithData {
    PrintWithData(Data data) : data(data) {}

    template<typename T>
    operator()(const T& thingToBePrinted)
    {
        std::cout << thingToBePrinted << std::endl;
    }

    Data data;
};

int main()
{
    MyStruct s;
    //this will compile
    boost::fusion::for_each(s, PrintWithData<std::string>("here I will pass my data"));
}