Re: fusion pair issue?

On 27-03-17 17:34, Patrick Welche wrote:
> Given the trivial working attached code, I do the following:
>
> --- works.cpp	2017-03-27 17:25:13.008492450 +0200
> +++ fails.cpp	2016-06-14 13:17:12.683679158 +0200
> @@ -2,16 +2,17 @@
>  
>  #include <boost/spirit/home/x3.hpp>
>  #include <boost/fusion/include/adapt_struct.hpp>
> +#include <boost/fusion/include/std_pair.hpp>
>  
>  namespace x3 = boost::spirit::x3;
>  
>  struct result
>  {
> -	std::string first, second;
> +	std::pair<std::string, std::string> both;
>  };
>  
>  BOOST_FUSION_ADAPT_STRUCT(result,
> -	first, second
> +	both
>  )
>  
>  int main()
> @@ -27,8 +28,8 @@
>  		std::cout << "Bit left over at the end: "
>  		          << std::string(iter, end) << std::endl;
>  	else
> -		std::cout << "found: " << res.first << ' '
> -		                       << res.second << std::endl;
> +		std::cout << "found: " << res.both.first << ' '
> +		                       << res.both.second << std::endl;
>  
>  	return 0;
>  }
>
>
> and get a compiler error. What have I forgotten to change?
>
> (Hoping to use the automatic semantic action feature of x3. I'm sure I
> could write a lot more code and have it work, but I don't see why a priori
> the above isn't sufficient...)

Equivalent would be

    #define BOOST_SPIRIT_X3_DEBUG

    #include <boost/fusion/include/std_pair.hpp>
    #include <boost/spirit/home/x3.hpp>

    namespace x3 = boost::spirit::x3;

    using result = std::pair<std::string, std::string>;


See http://coliru.stacked-crooked.com/a/5e266b02bf68272a

Alternatively use:


    struct result : std::pair<std::string, std::string> {};
    BOOST_FUSION_ADAPT_STRUCT(result, first, second)



See http://coliru.stacked-crooked.com/a/674c614ed7f75e70

Or

    result res;
    bool ok = x3::parse(iter, end, +x3::alnum >> ' ' >> +x3::alnum,
res.both);

See http://coliru.stacked-crooked.com/a/2a847ad1037640f3

Or even more mixages:

    struct result
    {
        std::pair<std::string, std::string> both;
    };

    BOOST_FUSION_ADAPT_STRUCT(result, both.first, both.second)


See http://coliru.stacked-crooked.com/a/96ddef3f1dcba167

Last one, in case you really need to force automatic attribute
propagation without any Fusion sequence unpacking hints:

    result res;
    auto const p = x3::rule<struct _, decltype(result::both)> {}
                 = +x3::alnum >> ' ' >> +x3::alnum;
    bool ok = x3::parse(iter, end, p, res);

See http://coliru.stacked-crooked.com/a/020b2510b47aa467

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