Re: [boost] [POSSIBLE BUG] boost::fusion::fold des not work as advertised

From: Tobias Schwinger (tschwinger_at_[hidden])
Date: 2007-09-15 09:22:39

Marco Costalba wrote:
> struct make_string
> {

>     template<typename T, typename State>
>     struct result
>     {
>         typedef std::string type;
>     };

Seems the docs have not all been updated, yet.

This is the old result computation protocol. Today Fusion uses the 
std::result_of convention.

In this case it's sufficient to replace the above code with

      typedef std::string result_type;

For more complex result computation one can still use a nested 'result' 
metafunction, but it's always unary now and invoked with the signature:

      template< typename Signature >
      struct result;

      template< class Self, typename T0, typename T1 >
      struct result< Self(T0,T1) >
      {
         typedef /*...*/ type;
      };

Regards,
Tobias