htmlpurifier/library/HTMLPurifier/StringHash.php

<?php

/**
 * This is in almost every respect equivalent to an array except
 * that it keeps track of which keys were accessed.
 *
 * @warning For the sake of backwards compatibility with early versions
 *     of PHP 5, you must not use the $hash[$key] syntax; if you do
 *     our version of offsetGet is never called.
 */
class HTMLPurifier_StringHash extends ArrayObject
{
    protected $accessed = array();

    /**
     * Retrieves a value, and logs the access.
     */
    public function offsetGet($index) {
        $this->accessed[$index] = true;
        return parent::offsetGet($index);
    }

    /**
     * Returns a lookup array of all array indexes that have been accessed.
     * @return Array in form array($index => true).
     */
    public function getAccessed() {
        return $this->accessed;
    }

    /**
     * Resets the access array.
     */
    public function resetAccessed() {
        $this->accessed = array();
    }
}