使用函数在PHP中初始化列表

Question

I am trying to add a trait for auth longin functionality in laravel. Please can anyone explain to me the meaning of : Redirection and the reason why it works in php 7 but not 5.5? And is there anyway to make it work in PHP 5.5. Thank you

use Illuminate\Http\RedirectResponse as Redirection;


trait AuthenticatesUsers
{

    public function login(Request $request, Auth $auth) : Redirection
    {
    $authorized = $auth->guard($this->guard)->attempt($request->only('username', 'password'));

        if($authorized){
            return redirect($this->redirectTo);
        }
        return back()->with('authError', 'Login ID or Password is incorrect.')
                 ->withInput($request->except('password'));
    }

}