<?php
class BookShelf implements Aggregate 
{
	private $books;

	public function __construct() {
		$this->books = array();
	}
	public function & getBookAt( $index ) {
		return $this->books[$index];
	}
	public function appendBook( &$book ) {
		array_push($this->books, $book);
	}
	public function getLength() {
		return count($this->books);
	}
	public function iterator() {
		return new BookShelfIterator($this);
	}
}
?>