Question

I’ve overloaded the operator- (and -=) for 2D vectors (and scalars):

Vector2D Vector2D::operator-(const Vector2D& rhs) {
    return Vector2D(this->GetX() - rhs.GetX(), this->GetY() - rhs.GetY());
}

In order to get this call to not complain that no operator '-' matches these arguments I had to do this:

a2de::Vector2D Vector2D::GetFacingVector(const Vector2D& target, const Vector2D& source) {
    a2de::Vector2D facingVec(const_cast<Vector2D&>(target) - const_cast<Vector2D&>(source));
    return facingVec;
}

Or this:

a2de::Vector2D Vector2D::GetFacingVector(const Vector2D& target, const Vector2D& source) {
    a2de::Vector2D facingVec(Vector2D(target) - Vector2D(source));
    return facingVec;
}

Both of which seem like a very bad thing to do. (Not-with-standing the phrase “only use const_cast when you know what you’re doing because the compiler will assume you do!”)

Are these correct or is there a better way to accomplish the same thing?

Answer 1

Your operator should be:

Vector2D Vector2D::operator-(const Vector2D& rhs) const

Note the const.