Question

Which is best practice (in this case):

bool Foo::operator==(const Foo& other) {
  return bar == other.bar;
}

// Implementation 1
bool Foo::operator!=(const Foo& other) {
  return bar != other.bar
}

// Implementation 2
bool Foo::operator!=(const Foo& other) {
  return !(*this == other);
}

For operators like >, <, <=, >= I would go with implementation 2 when possible. However, for != I think implementation 1 is better since another method call is not made, is this correct?

Answer 1

The second implementation has the notable constraint that == will always be the boolean opposite of !=. This is probably what you want, and it makes your code easier to maintain because you only have to change one implementation to keep the two in sync.