php函数参数类和接口

class  {}
class D extends  {}
class E {}
function f(C $c) {
    echo get_class($c)."n";
}
f(new C);
f(new D);
f(new E);
?>

C
D
Fatal error: Uncaught TypeError: Argument 1 passed to f() must be an instance of C, instance of E given, called in - on line 14 and defined in -:8
Stack trace:
#0 -(14): f(Object(E))
#1 {main}
  thrown in - on line 8
?>

interface I { public function f(); }
class  implements I { public function f() {} }
// This doesn't implement I.
class E {}
function f(I $i) {
    echo get_class($i)."n";
}
f(new C);
f(new E);
?>

C
PHP Catchable fatal error:  Argument 1 passed to f() must implement interface I, instance of E given, called in /code/main.php on line 13 and defined in /code/main.php on line 8
?>