Re: [Boost-users] result_of protocol

Subject: Re: [Boost-users] result_of protocol
From: Hicham Mouline (hicham_at_[hidden])
Date: 2010-02-26 05:37:24

-----Original Message-----
>From: "Hicham Mouline" [hicham_at_[hidden]]
>Date: 26/02/2010 09:40 AM
>To: boost-users_at_[hidden]
>Subject: Re: result_of protocol.

>----------------------------------------------------------------------------------
>struct extract_rule {
>
 > template <typename Sig> struct result;
>
 > template <typename Holder>
 >struct result< extract_rule(const Holder) > {
 > typedef const typename Holder::type& type;
>  };

>  template <typename Holder>
>  typename result< extract_rule(const Holder) >::type
>  operator()( const Holder& h ) const
>  {
>    return h.rule;
>  }
>};
>----------------------------------------------------------------------------------

>1>        with
>1>        [
>1>            Sig=extract_rule (const onevariantrule<parameters_t,0,boost::spirit::istream_iterator> )
>1>        ]

>The template onevariantrule<> is defined _before_ extract_rule.

>-------------------------------------------------------------------------------------------
>template <typename parameters_t, unsigned n, typename Iterator> 
>struct onevariantrule {
>  typedef .... type;
>};
>-------------------------------------------------------------------------------------------

>Holder matches onevariantrule<parameters_t,0,boost::spirit::istream_iterator>.
>That template instantiation is indeed a class.

In the snippet above, I replaced Holder by what the compiler tells me it is in the error log, as

------------------------------------------------------------
struct extract_rule {

template <typename Sig> struct result;

template <typename Holder>
struct result< extract_rule(const Holder) > {
typedef const onevariantrule<parameters_t,0,boost::spirit::istream_iterator>::type& type;
};
------------------------------------------------------------
And this works.

If msvc is able to see that Holder is that particular template instantiation in the error log, isn't it able to know then that Holder is a class?

regards,