在 Laravel 5 中 app.PHP 中配置文件 providers 中类后面为什么跟一个::class

    'providers' => [

        /*
         * Laravel Framework Service Providers...
         */
        Illuminate\Foundation\Providers\ArtisanServiceProvider::class,
        Illuminate\Auth\AuthServiceProvider::class,
        Illuminate\Broadcasting\BroadcastServiceProvider::class,
        Illuminate\Bus\BusServiceProvider::class,Copy