} interface c extends a, b { public function baz(); } class d implements c { public function foo($a) { if (!isset($a)) { return "foo"; } else { return $a; } } public function bar() { return "bar"; } public function baz() { return "baz"; } } $d = new d(); echo $d->foo("tes"); echo "<br>"; echo $d->bar(); echo "<br>"; echo $d->baz(); echo "<br>";