public static function toArray() : array
    {
        if (static::$array == null) {
            $ref = new \ReflectionClass(static::class);
            $consts = $ref->getConstants();
            static::$array = array();
            foreach ($consts as $key => $value) {
                if (stripos($key, 'VALUE_') === 0) {
                    static::$array[$key] = $value;
                }
            }
        }

        return static::$array;
    }