asdasd

asdasd.php

class A {
   public function bar() : int {}
}

class B extends A {
   public function bar() : void {}
}

function foo(A $bar) {
	// prepare to be surprised when $bar is instance of B
	$value = $bar->bar();
}

if (rand(0, 1)){
    $object = new A();
}
else {
    $object = new B();
}

foo($object);