CODEWITHSUNDEEP
c++
stoneyan
stoneyan

Reputation: 871

overload operator followed by template type parameters

In boost::unordered_map, the template is declared like this:

template <class K, class T, class H, class P, class A>
class unordered_map
{

and at the bottom of the template, there's a method declared like this:

    friend bool operator==<K,T,H,P,A>(
            unordered_map const&, unordered_map const&);

Could anyone please tell me why <K, T, H, P, A> is needed here?

Thanks!

Upvotes: 0

Views: 48

Answers (1)

T.C.
T.C.

Reputation: 137404

As written, the line declares as a friend a particular specialization of the operator== function template declared previously as

template <class K, class T, class H, class P, class A>
bool operator==(unordered_map<K, T, H, P, A> const&,
    unordered_map<K, T, H, P, A> const&);

If you remove the <K,T,H,P,A> -

friend bool operator==(unordered_map const&, unordered_map const&);

Then it would instead befriend a non-template function operator==, separate and distinct from the function template, which would be incorrect.

(The relevant standardese is found in §14.5.4 [temp.friends]/p1.)

Upvotes: 2

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