laravel的一个依赖注入的例子中一段代码没看懂。

interface UserRepositoryInterface
{
    public function all();
}Copy

class DbUserRepository implements UserRepositoryInterface
{
    public function all()
    {
        return User::all()->toArray();
    }
}Copy

class UserController extends BaseController
{
    public function __construct(UserRepositoryInterface $users)
    {
        $this->users = $users;
    }

    public function getIndex()
    {
        $users=$this->users->all();
        return View::make('users.index', compact('users'));
    }
}Copy