Re: [boost] [Proto] Access to member in proto expression tree

From: Eric Niebler (eric_at_[hidden])
Date: 2007-07-07 23:52:06

Replying to myself ...

Eric Niebler wrote:
>      template<typename Expr>
>      struct Expression<Expr, typename enable_if<matches<Expr, DoGrammar> 
>  >::type>
>        : extends<Expr, Expression<Expr>, Domain>
>      {
>          explicit Expression(Expr const &expr = Expr())
>            : extends<Expr, Expression<Expr>, Domain>(expr)
>            , while_(make_expr<WhileTag, Domain>(This()))
>          {}
> 
>          using extends<Expr, Expression<Expr>, Domain>::operator =;
>          typename proto::result_of::make_expr<WhileTag, Domain, 
> Expression const>::type while_;
> 
>      private:
>          Expression const &This() const { return *this; }
>      };
> 
>      struct DoWhileGrammar
>        : function<
>              unary_expr<
>                  WhileTag
>                , DoGrammar
>              >
>            , Grammar
>          >
>      {};

Or perhaps try the following, which is a little cleaner IMO ...

     template<typename Expr>
     struct Expression<Expr
       , typename enable_if<matches<Expr, DoGrammar> >::type
     >
       : extends<Expr, Expression<Expr>, Domain>
     {
         explicit Expression(Expr const &expr = Expr())
           : extends<Expr, Expression<Expr>, Domain>(expr)
         {}

         using extends<Expr, Expression<Expr>, Domain>::operator =;

         template< typename A0 >
         typename proto::result_of::make_expr<
             WhileTag, Domain, Expression const, A0 const
         >::type const
         while_(A0 const &a0) const
         {
             return make_expr<WhileTag, Domain>(*this, a0);
         }
     };

     struct DoWhileGrammar
       : binary_expr<
             WhileTag
           , DoGrammar
           , Grammar
         >
     {};

HTH,

-- 
Eric Niebler
Boost Consulting
www.boost-consulting.com