CollectionUsingSplObjectStorage.php

<?php declare(strict_types = 1);

class XCollection implements Countable, IteratorAggregate
{
	/**
	 * @var SplObjectStorage
	 */
	private $x;

	public function __construct()
	{
		$this->x = new SplObjectStorage();
	}

	public function add(X $x)
	{
		$this->x->attach($x);
	}

	public function remove(X $x)
	{
		$this->x->detach($x);
	}

	public function getIterator()
	{
		return $this->x;
	}

	public function count()
	{
		return count($this->x);
	}

	public function sort()
	{
		$array = iterator_to_array($this->x);
		uasort($array, function ($elementA, $elementB) {
			return $elementA->y() <=> $elementB->y();
		});
		$this->x = new SplObjectStorage();
		foreach ($array as $element) {
			$this->x->attach($element);
		}
	}
}