polymorphism relates inheritance [closed]

Answer 1

Providing your interfaces match you don't need to use inheritance.

It's easier to ensure interfaces match and provide a guarantee by using a contract such as subclassing a base class that has abstract methods (that you have to provide an implementation for in your subclass) or implement a shared interface.

Interfaces don't contain any code, they're just what they say on the tin - a blueprint for a certain interface. Base classes can contain some implementation but abstract classes and methods must be derived / subclassed to be used.

Then you can apply type hints to check for a common Interface or base class (Observer):

public function register(Observer observer) {

    observers.push(observer);

}

or check an Interface is implemented:

if (class instanceof MyInterface) {
    // call a method that exists in your interface
    class.myMethod();
}

or your object extends a base-class that has certain abstract methods:

if (class instanceof MyBaseClass) {
    class.guaranteedToExist();
}