From: rogeeff (rogeeff_at_[hidden])
Date: 2002-02-23 11:30:37
--- In boost_at_y..., Aleksey Gurtovoy <alexy_at_m...> wrote:
> David Abrahams wrote:
> > > But you still end up with the following ambiguity on MSVC:
> > >
> > > template<typename T>
> > > struct A {
> > > };
> > >
> > > template<typename T>
> > > void foo( T const& ) {}
> > >
> > > template<typename T>
> > > void foo( A<T> const& ) {}
> > >
> > > int main(int, char*[])
> > > {
> > > A<int> a_int;
> > >
> > > foo( a_int );
> > >
> > > return 0;
> > > }
> > >
> > > error C2667: 'foo' : none of 2 overload have a best conversion
> > >
> > > Anyone knows a fix?
> >
> > It depends whether 'A' is supposed to represent a
> > user-defined type or a template supplied by the library. If the
> > latter, you can intrude on foo and detect that T is an A<T> using
> > the sizeof() trick, then dispatch as appropriate. Otherwise, I'm
> > afraid there's no way.
>
> #include <iostream>
>
> template< typename T > struct A {};
>
> namespace aux {
> template< typename T >
> struct foo_impl
> {
> template< typename U >
> static void foo(A<U> const&, long)
> {
> std::cout << "foo(A<U> const&)\n";
> }
>
> static void foo(T const&, int)
> {
> std::cout << "foo(T const&)\n";
> }
> };
> }
>
> template< typename T >
> void foo(T const& t)
> {
> aux::foo_impl<T>::foo(t, 1L);
> }
>
> int main()
> {
> foo(int());
> foo(A<int>());
> return 0;
> }
>
> That's more, I belive that the technique allows you to simulate
partial
> ordering of any number of overloaded function templates, not just 2
of them.
>
> Aleksey
Could you explain how it is working ? What is the role of second
argument? Why long/int? Why 1L? How to extend this technique for more
then 2 cases.
Gennadiy.