scheme = $scheme; $this->value = $value; } public function __toString() { // There is no $this->data here return md5(serialize($this)); } public function get_scheme() { if ($this->scheme !== null) { return $this->scheme; } else { return null; } } public function get_value() { if ($this->value !== null) { return $this->value; } else { return null; } } }