Function that checks is user have specific role/roles

I want to proposed new function in core user.module to omit long code like this:

global $user;
if(in_array($role, array_values($user->roles)) {
  // .. do something
}

cleaner solution is

function user_is($roles) {
	global $user;
        if(is_array($roles)) {
               foreach($roles as $role) {
                      if(in_array($role, array_values($user->roles))) {
                                   return TRUE;
                      }
               }
        } else {
	       return in_array($role, array_values($user->roles));
        }
}

.. so u can use like this

if(user_is('employer')) { /* ..do something */ }

OR

if user is employer OR employee (have one of role in array)

if(user_is(array('employer', 'employee'))) { /* ..do something */ }