Helper function for sorting objects by props

Helpers.class.php

<?php 
class HelperLibrary
{
/** 
   * Sort an associative array of objects by any number of properties in any order, maintaining key association.
   *
   * Example usage, for an array of users:
   * 
   *   $users = array();
   * 
   *   $user = new stdClass;
   *   $user->name = 'John';
   *   $user->age = 45
   *   $users['a'] = $user;
   *
   *   $user = new stdClass;
   *   $user->name = 'Alex';
   *   $user->age = 20
   *   $users['b'] = $user;
   *
   *   $user = new stdClass;
   *   $user->name = 'Alex';
   *   $user->age = 39
   *   $users['c'] = $user;
   *
   *   $user = new stdClass;
   *   $user->name = 'Sarah';
   *   $user->age = 19
   *   $users['d'] = $user;
   *
   *   //Sort users by name ASC, age DESC
   *   HelperLibrary::osort($users, array('name'=>true, 'age'=>false));
   *   Alex   39
   *   Alex   20
   *   John   45
   *   Sarah  19
   *
   *   //Sort users by name DESC, age ASC
   *   HelperLibrary::osort($users, array('name'=>false, 'age'=>true));
   *   John   45
   *   Sarah  19
   *   Alex   20
   *   Alex   39
   *   
   * @author James Tarleton
   * @param  array $array 
   * @param  array $props : boolean values for each sort direction, keyed by property name
   * @return void
   */
  public static function osort(&$array, array $props) 
  {         
    $closure = function($a, $b) use ($props) { 
      foreach($props as $prop => $ascending){ 
        if($a->$prop != $b->$prop){ 
          if($ascending){
              return strtolower($a->$prop) > strtolower($b->$prop) ? 1 : -1; 
          } else {
              return strtolower($a->$prop) < strtolower($b->$prop) ? 1 : -1;
          }
        } 
      } 
      return -1; //if all props equal        
    };

    uasort($array, $closure); 
  } 
}