PHP Strict Standards: Declaration of should be compatible

Question

I have the following hierarchy of classes:

class O_Base {...}

class O extends O_Base {...}

abstract class A_Abstract {
    public function save(O_Base $obj) {         


        

Answer 1

Change A_Abstract to

abstract class A_Abstract {
    public function save(O $obj) {...}
}

No matter that O is extended from O_Base, they are two different objects, and as A extends A_Abstract the save functions need to be compatible with each other, meaning you need to pass the same object in, O.