Subject: Re: [Boost-users] result_of protocol
From: Hicham Mouline (hicham_at_[hidden])
Date: 2010-02-26 06:26:07
>----------------------------------------------------------------------------------
>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.
Both specializations
template <typename Holder>
struct result< extract_rule(const Holder) > {
};
and
template <typename Holder>
struct result< extract_rule(const Holder& ) > { ///// the reference was missing here, doh!
typedef const typename Holder::type& type;
};
were needed.
Sorry for the spam,