依赖注入约束

<?php
/*依赖注入约束注入的类必需是实现visit接口的类*/
interface visit{
    public function go();

}
class car implements  visit{
    public function go(){
        echo '轮子跑';
    }
}
class train{
    public function go(){
        echo '动车组';
    }
}
class trive{
    public $visit;
    function __construct(visit $visit){//visit 接口的实现类
            $this->visit = $visit;
    }
    public function triveType(){
        $this->visit->go();
    }
}
$car = new car();
/*$trive = new trive($car);
$trive->triveType();*/
$train = new train();
$trive = new trive($train);
$trive->triveType();//报错 因为注入的train实例没有实现visit接口