Abstract.php

<?php

interface ProviderInterface
{
    public function foo();
}

abstract class AbstractProvider implements ProviderInterface
{
    public function bar()
    {
        return "bar\n";
    }

    // foo() is not implemented here
}

class MyProvider extends AbstractProvider
{
    public function foo()
    {
        return "foo\n";
    }
}

$provider = new MyProvider;
echo $provider->foo(); // foo
echo $provider->bar(); // bar

I agree with @willdurand. But I understand your point of view...

The current implementation is not wrong at all. But yes, AbstractProvider should perhaps be named AbstractProviderTools or somthing like that. Personally, I do prefer AbstractProvider ;)

Anyway it is a very good question. I don't know what the best practice here.

Naa, it's an abstract class, not an abstract implementation of a provider. If I needed an abstract implementation of a provider, that abstract class would implement the ProviderInterface, and this abstract class would implement the methods (partially or not) of this interface. Is it the case? No, because of that.

So no need to add an interface on such an abstract class. As it is abstract, I can't instantiate it, so naming is correct here. I do prefer having the interface defined in the concrete implementation, than somewhere hidden in an abstract class. If the class was named BaseProvider, thing would be different.

If I want to drop the abstract class for some reasons, I can, and all concrete providers will still fit the interface. What is important is that concrete providers implement the interface, that is the contract.

I totaly agree :)

I do prefer having the interface defined in the concrete implementation

This implementation gives flexibility :)

If I want to drop the abstract class for some reasons, I can

Thanks for this explanation.