Php type hinting not getting along with interfaces and abstract classes?

Question

I think it\'ll be much easier to see the problem in a code example than writing the question in the first place. Here is my php code:

Answer 1

php doesn't seem to be recognizing the signatures of AnAbstractClass::method and ConcreteClass::method as compatible.

PHP is correct, they're not compatible. By allowing only instances of AClass (or its children) to be passed to ConcreteClass::method, you're breaking the contract that AnAbstractClass provides: Any of its subclasses must accept AnInterface as an argument to its method().

If your example worked, and I had another class BClass implementing AnInterface, we'd have a situation where according to AnAbstractClass, method() should accept instances of BClass, while according to ConcreteClass, it shouldn't.

Change your signature for ConcreteClass::method to match that of AnAbstractClass::method.