Re: [Boost-users] fusion::result_of::transform<Seq1, Seq2, F> -- argument dependent result type

Subject: Re: [Boost-users] fusion::result_of::transform<Seq1, Seq2, F> -- argument dependent result type
From: e r (erwann.rogard_at_[hidden])
Date: 2008-09-12 23:48:39

e r wrote:
> Steven Watanabe wrote:
>> AMDG
>>
>> e r wrote:
>>> // probably not what result_of::transform expects, based on compile
>>> // errors (below)
>>>   template<typename Metafun,typename Arg2>
>>>   struct result{
>>>      typedef typename Metafun::type type;
>>>   };
>>>   
>> Fusion uses Boost.ResultOf.
>> http://www.boost.org/doc/libs/1_36_0/libs/utility/utility.htm#result_of
>>
>> In Christ,
>> Steven Watanabe
> 
> Thanks. I read the link above before posting as well as the proposal:
> 
> //example from proposal.
> struct square_ {
>   template<typename T> struct result {
>     typedef T type;
>   }
> 
>   template<typename T> T operator()(T& x) const
>   {
>     return x*x;
>   }
> };
> 
> but I'm not qualified enough to deduce the right answer in my case. i
> thought id would be like this:
> 
> template<typename Arg1>
> struct fun{
>   template<typename Metafun,typename Arg2>
>   struct result{
>      typedef typename Metafun::type type;
>   };
> 
>   template<typename Metafun,typename Arg2>
>   typename Metafun::type
>   operator()(const Metafun& meta,const Arg2& arg2)const{
>       typedef typename Metafun::type result_type;
>       return result_type(args,arg2);
>   }
> };
> 
> but apparently it's not correct. I guess I can't fully make sense of
> F::result<F(T1, T2, ..., TN)>::type. any hint here would be really helpful.
> 
> thanks!

I may have made a little bit of progress here...

struct fun{

 template<typename Signature> struct result;

 template<typename A>
 struct result<fun(const A&)>{
    typedef A type;
 };

 template<typename A>
 A operator()(const A& a)const{
    return A();
 };
};

typedef boost::result_of<fun(const my&)>::type result_type;

    BOOST_MPL_ASSERT(
        (
            mpl::is_same<
                result_type,
                my
            >
        )
    );