Re: [Boost-users] [Proto] Accessing inner types in transform

Subject: Re: [Boost-users] [Proto] Accessing inner types in transform
From: Eric Niebler (eric_at_[hidden])
Date: 2008-11-02 20:13:33

Joel Falcou wrote:
> So i may have missed something.
> 
> Here is the transform :
> 
>  struct C_base
>  : bp::or_< bp::when< bp::terminal<std::pair<arithmetic_grammar
>                                             ,arithmetic_grammar>
>                                   >
>                     , first_(bp::_)

You mean first_(bp::_value) here, right?

>                     >
>           , bp::when< bp::terminal<i_value>, int()>
>           , bp::when< arithmetic_grammar, bp::_value()>
>           , bp::when< bp::unary_expr<bp::_,C_base>,C_base(bp::_child)>
>           , bp::when< bp::binary_expr<bp::_
>                                      ,arithmetic_grammar
>                                      ,arithmetic_grammar
>                                      >
>                     , 
> binary_result<arithmetic>(C_base(bp::_left),C_base(bp::_right) )
>                     >
>           > {};
> 
> 
> here is first_
> 
>  struct first_ : bp::callable
>  {
>    template<class Sig> struct result;
>    template<class This, class Pair>
>    struct result<This(Pair)>
>    {
>      typedef typename boost::remove_reference<Pair>::type::first_type type;
>    };

You'll need to define an operator() here, or else you'll get an error if 
you actually use the transform for anything other than a type computation.

>  };
> 
> 
> Now when I try to get the C_base of a terminal, i got :
> erreur: no type named «proto_base_expr» in «struct std::pair<float, float>
> and other similar error.
> 
> What did I missed ?

HTH,

-- 
Eric Niebler
BoostPro Computing
http://www.boostpro.com