<?php



class Serializer{
    private  $data = [];

    /**
     * Serializer constructor.
     * @param array $data
     */
    public function __construct(array $data)
    {
        $this->data = $data;
    }

    public function  toJSONString(){
        return json_encode($this->data);
    }

    public function  toXLMString(){
        $xml = new SimpleXMLElement('<root/>');
        array_walk_recursive($this->data, array ($xml, 'addChild'));
        return $xml->asXML();
    }

    public function  toQueryString(){
        return http_build_query($this->data);
    }

}

abstract class CustomField{
    private static $data = [];

    /**
     * @return Serializer
     */
    public static function retrieve()
    {
        return new Serializer(self::$data);
    }
}

CustomField::retrieve()->toJSONString();
CustomField::retrieve()->toXLMString();
CustomField::retrieve()->toQueryString();