CollectionUsingArray.php

<?php declare(strict_types = 1);

class XCollection implements Countable, IteratorAggregate
{
	/**
	 * @var X[]
	 */
	private $x;

	public function __construct()
	{
		$this->x = [];
	}

	public function add(X $x)
	{
		$this->x[] = $x;
	}

	public function remove(X $x)
	{
		$key = array_search($x, $this->x);
		if ($key !== false) {
			unset($this->x[$key]);
		}
	}

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

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

	public function sort()
	{
		uasort($this->x, function ($elementA, $elementB) {
			return $elementA->y() <=> $elementB->y();
		});
	}
}