class Base {
    public function Base($a, $b) {
        echo $a+$b;
    }


    public function sayHello() {
        echo 'Hello ';
    }
}


trait SayWorld {
    public function SayWorld($a, $b, $c = 0) {
        echo (int)$c * ($a+$b);
    }

    public function sayHello($a = null) {
        parent::sayHello();
        echo 'World!'.$a;
    }
}

class MyHelloWorld extends Base {
    use SayWorld {
      SayWorld::SayWorld insteadof Base;
    }
}

$o = new MyHelloWorld(2, 3);
$o->sayHello(1);