Re: [boost] [mpl] has_template_xxx patch

From: Daniel Walker (daniel.j.walker_at_[hidden])
Date: 2007-03-30 10:13:39

Hello,

I've been looking into getting member template detection to work on
various compilers, and I have a question regarding SFINAE. I hope
someone can help. All the compilers I've tried reject the following.

template<class T>
struct foo {};

template<class T, class U>
void f(T,U) {}

template<class T, class U>
void f(foo<T,U>) {}         // error: wrong number of template
                            // arguments (2, should be 1) provided for
                            // 'template<class T> struct foo'

template<class T, class U>
struct bar {};

template<class T, class U>
struct bar<foo<T,U>, U> {}; // error: wrong number of template
                            // arguments (2, should be 1) provided for
                            // 'template<class T> struct foo'

int main()
{
    f(0,0);
    typedef bar<int,int> type;
}

Is this a substitution failure? Should the 2nd overload of f() be
removed from the set of candidate functions during overload
resolution? Should something similar be true for the partial
specialization of bar<>? Or is this standard compliant behavior?

I've worked out pretty much every other issue, but I don't think I can
get this one to work if this is a compiler bug.

Thanks.
Daniel