Description:
------------
Hint of return type in PHP works unexpected way.
It's not possible to change hint of return type to a more concrete subtype.

Test script:
---------------
interface Person {/* _ */}

interface PersonFactory
{
    public function createPerson(): Person;
}

class Customer implements Person {/* _ */}

class CustomerFactory implements PersonFactory
{
    public function createPerson(): Customer // PHP Fatal error:
    {                                        // Declaration of CustomerFactory::createPerson(): Customer
        return new Customer();               // must be compatible with PersonFactory::createPerson(): Person
    }
}