Implement Services Interface

[XedinUnknown]

This implements dhii/services-interface. Also, see container-interop/service-provider#53.

[mecha]

Rather than having Factory and Extension implement ServiceInterface, why not have the Service base class implement the interface and remove the duplicate abstract __invoke method? That way we avoid any signature conflicts between the Service class and the interface.

[XedinUnknown]

why not have the Service base class implement the interface

Because it is abstract. I don't want to impose an interface on an abstract class.

remove the duplicate abstract __invoke method

Missed that, thanks!

[mecha]

Because it is abstract. I don't want to impose an interface on an abstract class.

I don't understand. The purpose of the class is to reduce duplicate code between Factory and Extension. It's not really "imposing" if it's by design. But if you have strong feelings against this, I won't argue.