Re: [Boost-users] Proto: extending the example mixed.cpp

Subject: Re: [Boost-users] Proto: extending the example mixed.cpp
From: Eric Niebler (eric_at_[hidden])
Date: 2008-12-11 16:47:23

Kim Kuen Tang wrote:
> Hi all,
> 
> i wnat to extend the example in the file mixed.cpp with an operator[]:
> 
> double operator []( std::ptrdiff_t i ) const
>    {
>        DereferenceCtx const deref = {};
>        AdvanceCtx adctx(i); //just shift the iterator with std::advance
>        typename boost::result_of<Begin(Expr const &)>::type expr2 = 
> Begin()(*this);
>        proto::eval(expr2,adctx);
>        return proto::eval(expr2, deref);
>    }
> This works well.
> 
> However is it possible to let proto figure out what the result_type of 
> this function is?
> 
> I've tried to program in this way.
> 
> typedef typename boost::result_of<Begin(Expr const &)>::type Expr2;
>    typedef typename proto::result_of::eval<Expr,DereferenceCtx>::type 
<snip>

You probably need something like this:

     typedef
         typename boost::remove_reference<
             typename boost::result_of<Begin(Expr const &)>::type
         >::type
     Expr2;

     typedef
         typename proto::result_of::eval<Expr2, DereferenceCtx>::type
     result_type;

HTH,

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