Re: [boost] [config] BOOST_DEDUCED_TYPENAME

From: Peter Dimov (pdimov_at_[hidden])
Date: 2003-03-05 06:10:35

David Abrahams wrote:
> I was just getting ready to propose a new config macro called
> BOOST_ARG_DEPENDENT_TYPENAME based on this test:
> 
>     struct id { typedef int type; };
> 
>     template <class T> struct foo;
> 
>     template <class T>
>     void f(T)
>     {
>        typedef foo<typename T::type> y;
>     }
> 
>     int main()
>     {
>         f(id());
>         return 0;
>     }
> 
> But it turns out that this test is very similar to the one for
> BOOST_DEDUCED_TYPENAME, and in fact it finds the same compiler (VC6).
> So I guess the question is, do we currently have the right name for
> the test and macro?  VC6 will support typename on template arguments
> in some contexts:
> 
> 
>     struct id { typedef int type; };
> 
>     template <class T>
>     void f(T)
>     {
>        typedef typename T::type x;
>     }
> 
>     int main()
>     {
>         f(id());
>         return 0;
>     }

This means that you could have rewritten the above f as

template <class T>
void f(T)
{
    typedef typename T::type x;
    typedef foo<x> y;
}

Perhaps you should test

template <class T> foo<typename T::type> f(T);

instead, if that's what you need.