How to Properly Overload the Angle Bracket Operator for a Template Class?

Overloading the Angle Bracket Operator for a Template Class

Trying to overload the << operator as a friend to a template class Pair, one may encounter a compiler warning indicating a non-template function declaration. This issue arises due to a discrepancy between the friend declaration and the actual function definition.

To resolve this, one must specify that the friend declaration applies to a specialized instance of the template class Pair with specific template arguments. This is achieved by using empty angle brackets <> after the operator declaration in the friend declaration.

The corrected code looks like this:

<code class="cpp">template <class T, class U>
class Pair {
public:
    Pair(T v1, U v2) : val1(v1), val2(v2) {}
    ~Pair() {}
    Pair& operator=(const Pair&);
    friend ostream& operator<<<> (ostream&, Pair<T, U>&);

private:
    T val1;
    U val2;
};</code>

Additionally, the function definition for the overloaded operator must be declared before the template class definition, as follows:

<code class="cpp">template <class T, class U>
ostream& operator<<<> (ostream& out, Pair<T, U>& v);

template <class T, class U>
class Pair {
    // ...
};</code>

By making these changes, the compiler can correctly identify the friend function as a specialization for the Pair template and avoid the warning regarding a non-template function declaration.

The above is the detailed content of How to Properly Overload the Angle Bracket Operator for a Template Class?. For more information, please follow other related articles on the PHP Chinese website!