在构造中传递数据类型

I'am trying to pass a data of type string to a construct to ensure that a string is always passed

In my reset password class I have

class RequestResetPassword extends Mailable
  {

  public function __construct(User $user, String $resettoken)
   {

   }

The user part is okay as it is of type user Model but how do i go about the access token part by stating that it must always be a string

The above generates an error

App string not found.

It should be string (lowercase), since is not a class. Something like:

public function __construct(User $user, string $resettoken)
{

}

Check the PHP documentation on type declarations.