Re: [boost] [result_of] Usage guidelines

Subject: Re: [boost] [result_of] Usage guidelines
From: Mathias Gaunard (mathias.gaunard_at_[hidden])
Date: 2012-09-04 04:06:32

On 04/09/2012 08:59, Andrey Semashev wrote:
> I suppose, in such cases additional
> specializations are still needed:
>
>    struct my_foo
>    {
>      template< typename >
>      struct result;
>
>      template< typename ArgT >
>      struct result< my_foo(ArgT const&) >;

I assume you meant

template< typename ArgT >
struct result< my_foo(ArgT const&) >
{
   typedef ArgT type;
};

there?

>
>      template< typename ArgT >
>      struct result< my_foo(ArgT&) >
>      {
>        typedef ArgT type;
>      };
>
>      template< typename ArgT >
>      ArgT operator() (ArgT& arg) const
>      {
>        return arg;
>      }
>    };

1) doesn't support result_of<my_foo(int)>
2) not always the same type as what operator() returns (consider a const 
lvalue passed to operator())
3) needless repetition

You probably wanted to write

struct my_foo
{
   template<class Sig>
   struct result;

   template<class This, class A0>
   struct result<This(A0)> : strip<A0> {};

   template<class A0>
   typename remove_const<A0>::type operator()(A0& a0) const
   {
     return a0;
   }
};