LaravelのRouteパラメータにバリデーションをつけたいとき

https://laravel.com/docs/5.6/routing#route-parameters のRegular Expression Constraints

Route::get('/admin/{role}', function ($role) {
    $list = Admin::all();
    return view('list', [
        "list" => $list,
        "role" => $role
    ]);
})->where("role","(admin|user)");

PHPで書く場合

Route::get('/admin/{role}', function ($role) {
    if(!in_array($role,[
        "admin",
        "user"
    ])){
        abort(404);
    }
    $list = Admin::all();
    return view('list', [
        "list" => $list,
        "role" => $role
    ]);
});