Force classes to implement one of a set of methods

Question

Let's say I need a group of classes to implement all of methods X, Y and Z to work properly. In that case, I can let them implement a common interface to force that.

Now, my case is a bit different - my classes need to implement at least one of X, Y and Z, not necessarily all of them. Interfaces can't help me here. The closest thing I can think of is a common parent - it can check the existence of X, Y or Z in its construcor.

I'd rather avoid inheritance here, because I may need to implement this "interface" in a class that already has a parent. So - is there another elegant way to do this?

(I am working in PHP, but if a general OOP solution exists, it may serve to a broader audience.)

Answer 1

I'd rather avoid inheritance here, because I may need to implement this "interface" in a class that already has a parent. So - is there another elegant way to do this?

If I understood you correctly, you can solve that issue through Traits:

trait DefaultImpl
{
    public function x()
    {
        echo "Default implementation of x()\n";
    }

    public function y()
    {
        echo "Default implementation of y()\n";
    }

    public function z()
    {
        echo "Default implementation of z()\n";
    }
}

class XImpl
{
    use DefaultImpl;

    public function x()
    {
        echo "Custom implementation of X\n";
    }
}

$x = new XImpl();
$x->x();
$x->y();
$x->z();

It's not a very good solution from design point of view. But it's better than unnecessary inheritance.