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<?php class A {} class B extends A {} class C extends B {} class D {} interface InterfaceTest { public function foo($d); } abstract class AbstractTest { public abstract function foo($d); } class TestAbstractContravariance extends AbstractTest { public function foo($d) : D {} } class TestAbstractCovariance extends AbstractTest { public function foo($d) : D {} } class TestInterfaceContravariance implements InterfaceTest { public function foo($d) : D {} } class TestInterfaceCovariance implements InterfaceTest { public function foo($d) : D {} }