template instantiation trouble

From: Alexander Stippler (stip_at_mathematik.uni-ulm.de)
Date: 12/31/03 

Date: Wed, 31 Dec 2003 14:05:22 +0100

Hello,

I wrote an (templatized) operator==() and don't know why the compiler
doesn't consider it. What prevents it from being chosen?

class Data {};

template <typename D>
class Vector
{
    public:
        typedef Data ConstType;
        typedef Data Type;
};

template <typename D>
bool
operator==(const typename Vector<D>::ConstType &lhs,
           const typename Vector<D>::Type &rhs)
{
    return true;
}

// this operator is chosen, if added.
//bool
//operator==(const Vector<Data>::ConstType &lhs,
// const Vector<Data>::Type &rhs)
//{
// return true;
//}

int
main()
{
    Vector<Data>::ConstType ct;
    Vector<Data>::Type t;

    ct == t;

    return 0;
}

What is not standard conforming, what is not allowed here?

regards,
        alex

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