Set.php

<?php

class Stripe_Util_Set
{
  private $_elts;

  public function __construct($members=array())
  {
    $this->_elts = array();
    foreach ($members as $item)
      $this->_elts[$item] = true;
  }

  public function includes($elt)
  {
    return isset($this->_elts[$elt]);
  }

  public function add($elt)
  {
    $this->_elts[$elt] = true;
  }

  public function discard($elt)
  {
    unset($this->_elts[$elt]);
  }

  // TODO: make Set support foreach
  public function toArray()
  {
    return array_keys($this->_elts);
  }
}