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)

Yes. It did not work. Because... of `abstract public function b();` in the second class. Without it it goes. Question answered — Jakub M., Sep 01 '11 at 11:36
@ied3vil Traits were not yet available in PHP when the question was posted. — faintsignal, Apr 12 '19 at 16:36
Don't forget, abstract functions override is allowed from PHP 7.2 only ! — Vladimir Ch, Feb 18 '21 at 18:27

score 42 · Accepted Answer · answered Sep 01 '11 at 11:33

42

Yes, this is possible.

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

answered Sep 01 '11 at 11:33

Arnaud Le Blanc

95,062
22
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2

without `abstract public function b();` in the second class it works... answered, thanks – Jakub M. Sep 01 '11 at 11:37
Note that the order of the definitions matters. If you put the class VeryConcrete first, you will get 'Fatal error: Class 'MoreConcrete' not found' error. Be careful not to put the abstract cart before the horse. – RightHandedMonkey Sep 11 '14 at 15:31

score 6 · Answer 2 · answered Sep 23 '13 at 07:23

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(); }
}

score 5 · Answer 3 · answered Sep 01 '11 at 11:37

5

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

Here is more detailed explanation.

answered Sep 01 '11 at 11:37

matino

16,442
7
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php abstract class extending another abstract class

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