Re: Class templates and friend function templates

BigMan wrote:
> I have a class template like this:
>
> template< typename t >
> class c;
>
> I'd also like to have an operator == for objects of types, which are
> different specializations of c:
> template< typename t1, typename t2 >
> bool operator ==
> (
> s< t1 > const&
> , s< t2 > const&
> );
>
> In order to implement this operator, I need it to be a friend of both
> s< t1 > and s< t2 >. For the sake of safety, I'd like no other
> specialization of c to have this operator as its friend. Is this
> possible and, if so, how?

Like this:

// Code
template <class T> class C;

template <class U, class V> bool operator ==(C<U>,C<V>);

template <class T> class C
{
public: C(int x_) : x(x_) {}

private: int x;

template <class U,class V>
friend bool operator == <T>(U u, V v);
};

template <class U, class V>
bool operator == (C<U> u, C<V> v)
{
return u.x == v.x;
}

int main()
{
C<int> c1(1);
C<float> c2(2);
bool b = c1 == c2;
}
// End of code

I'm actually not sure that this code is standard conforming, although it
seems like it should be. VC 7.1 likes it, but Comeau claims that the
template friend declaration is ill-formed.

-cd




.

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