JsonSerializable.php

<?php

if (!interface_exists('JsonSerializable')) {
    interface JsonSerializable
    {
        /**
         * Specify data which should be serialized to JSON.
         *
         * @link http://php.net/manual/en/jsonserializable.jsonserialize.php
         *
         * @return mixed data which can be serialized by <b>json_encode</b>,
         *               which is a value of any type other than a resource.
         *
         * @since 5.4.0
         */
        public function jsonSerialize();
    }
}