Template woos

[André Pönitz]

// The following works:

template <class S, class Base>
struct IsDerivedFrom {
        struct No {};
        struct Yes { No n_[3]; };
        struct Helper {
                 static Yes Test(Base*);
                 static No  Test(...);
        };
        enum { value = sizeof(Yes) == sizeof( Helper::Test(static_cast<S*>(0)) 
) };
};


// This does not but I think it should:

template <class S, class Base>
struct IsDerivedFrom {
        struct No {};
        struct Yes { No n_[3]; };
        static Yes Test(Base*);
        static No  Test(...);
        enum { value = sizeof(Yes) == sizeof( Test(static_cast<S*>(0)) ) };
};

This is tested with 2.95 and 3.0.2 and both give the error
d.C: In instantiation of `IsDerivedFrom<X, HasBar>':
d.C:48:   instantiated from `void foo(const T&) [with T = X]'
d.C:56:   instantiated from here
d.C:48: invalid use of undefined type `struct IsDerivedFrom<X, HasBar>'
d.C:21: forward declaration of `struct IsDerivedFrom<X, HasBar>'

(with different line numbers, though)
Is this a compiler bug or is the code indeed wrong?

Andre'


-- 
André Pönitz .............................................. address@hidden