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

3 Nov 2008


      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