oop - PHP equivalent of friend or internal

Question

Is there some equivalent of "friend" or "internal" in php? If not, is there any pattern to follow to achieve this behavior?

Edit: Sorry, but standard Php isn't what I'm looking for. I'm looking for something along the lines of what ringmaster did.

I have classes which are doing C-style system calls on the back end and the juggling has started to become cumbersome. I have functions in object A which take in object B as a parameter and have to call a method in object B passing in itself as an argument. The end user could call the method in B and the system would fall apart.

Answer 1

PHP doesn't support any friend-like declarations. It's possible to simulate this using the PHP5 __get and __set methods and inspecting a backtrace for only the allowed friend classes, although the code to do it is kind of clumsy.

There's some sample code and discussion on the topic on PHP's site:

class HasFriends
{
    private $__friends = array('MyFriend', 'OtherFriend');

    public function __get($key)
    {
        $trace = debug_backtrace();
        if(isset($trace[1]['class']) && in_array($trace[1]['class'], $this->__friends)) {
            return $this->$key;
        }

        // normal __get() code here

        trigger_error('Cannot access private property ' . __CLASS__ . '::$' . $key, E_USER_ERROR);
    }

    public function __set($key, $value)
    {
        $trace = debug_backtrace();
        if(isset($trace[1]['class']) && in_array($trace[1]['class'], $this->__friends)) {
            return $this->$key = $value;
        }

        // normal __set() code here

        trigger_error('Cannot access private property ' . __CLASS__ . '::$' . $key, E_USER_ERROR);
    }
}

(Code proved by tsteiner at nerdclub dot net on bugs.php.net)