php abstract class extending another abstract class

Question

Is it possible in PHP, that an abstract class inherits from an abstract class?

For example,

abstract class Generic {
    abstract public function a();
    abstract public function b();
}

abstract class MoreConcrete extends Generic {
    public function a() { do_stuff(); }
    abstract public function b(); // I want this not to be implemented here...
}

class VeryConcrete extends MoreConcrete {
    public function b() { do_stuff(); }

}

( abstract class extends abstract class in php? does not give an answer)

Answer 1

Yes, this is possible.

If a subclass does not implements all abstract methods of the abstract superclass, it must be abstract too.

Answer 2

Yes it is possible however your code would not work if you called $VeryConcreteObject->b()

Here is more detailed explanation.

Answer 3

It will work, even if you leave the abstract function b(); in class MoreConcrete.

But in this specific example I would transform class "Generic" into an Interface, as it has no more implementation beside the method definitions.

interface Generic {
    public function a(); 
    public function b();
}

abstract class MoreConcrete implements Generic {
    public function a() { do_stuff(); }
    // can be left out, as the class is defined abstract
    // abstract public function b();
}

class VeryConcrete extends MoreConcrete {
    // this class has to implement the method b() as it is not abstract.
    public function b() { do_stuff(); }
}