Online PHP editor | output for sZ9XB

<?php interface ParentInterface {} interface ChildInterface extends ParentInterface {} interface OriginalHandlerInterface { public function handle(ParentInterface $a): string; } interface AnotherHandlerInterface { public function handle(ChildInterface $a): string; } class RegularImplementor implements AnotherHandlerInterface { public function handle(ChildInterface $a): string { return class_name($a); } } class ContravariantImplementor implements AnotherHandlerInterface { public function handle(ParentInterface $a): string { return class_name($a); } } class OriginalImplementor implements OriginalHandlerInterface { public function handle(ParentInterface $a) : string { return class_name($a); } } // this will error out class WrongOriginalImplementor implements OriginalHandlerInterface { public function handle(ChildInterface $a) : string { return class_name($a); } }