Re: [boost] Fun, only handled by vc6/7!

From: Paul Mensonides (pmenso57_at_[hidden])
Date: 2003-01-11 23:47:59

----- Original Message -----
From: "David Abrahams" <dave_at_[hidden]>

> >> Here's an interesting turn-of-the-tables: I was experimenting with
> >> using SFINAE to disable conversion operators, and I discovered that
> >> almost every compiler except vc6/7 rejects this code:
> >>
> >> template <class T> struct voidify { typedef void type; };
> >> template <class T> struct Y {};
> >> struct X
> >> {
> >>     template <class T>
> >>     operator Y<T> (typename voidify<T>::type) const { return Y<T>(); }
> >> };
> >
> > Is this even legal?  I.e. for a user-defined conversion operator to have
any
> > arguments at all?
>
> Look twice; the argument is void.

I know, but I don't think you can derive a 'void' parameter list that way.
E.g.

template<class> struct test; // not defined

template<class T> struct test<void (*)(T)> { }; // defined

void f(void) { }

int main() {
    test< &f >(); // error
    return 0;
}

In other words, the "void" parameter list is fundamentally different than
"type void".

Paul Mensonides