The following code example is taken from the book
C++ Templates - The Complete Guide, 2nd Edition
by David Vandevoorde, Nicolai M. Josuttis, and Douglas Gregor,
Addison-Wesley, 2017
© Copyright David Vandevoorde, Nicolai M. Josuttis, Douglas Gregor 2017
template<typename Derived>
class EqualityComparable
{
public:
friend bool operator!= (Derived const& x1, Derived const& x2) {
return !(x1 == x2);
}
};
class X : public EqualityComparable<X>
{
public:
friend bool operator== (X const& x1, X const& x2) {
// implement logic for comparing two objects of type X
}
};
int main()
{
X x1, x2;
if (x1 != x2) { }
}