cocur / chain

src/Link/IntersectKey.php

<?php

namespace Cocur\Chain\Link;

use Cocur\Chain\Chain;

/**
 * IntersectKey.
 *
 * @author    Florian Eckerstorfer
 * @copyright 2015-2018 Florian Eckerstorfer
 */
trait IntersectKey
{
    /**
     * @param Chain|array $array
     *
     * @return self
     */
    public function intersectKey($array): self
    {
        $this->array = array_intersect_key($this->array, $array instanceof Chain ? $array->array : $array);

The property array does not exist. Although not strictly required by PHP, it is generally a best practice to declare properties explicitly.

        return $this;
    }
}