Variance and Signature Validation – basically in simple layman’s term – class return type

then interesting thing I find about the example from

class A {}

interface SomeInterface
{
    public function test() : A;
}

class B implements SomeInterface
{
    public function test() : A // all good!
    {
        return null;
    }

    public function test2() : string
    {
        return 'wow';
    }
}

// all good, will not fail
$b = new B();

// will fail with TypeError: 
// Return value of B::test() must be an instance of A, null returned 
// $b->test();

$b->test2(); // all good

more about php7:

if you need to install PHP7 check out this article

php7 null coalesce operator ??