[RFC] Magic Method that handles unset($object) View as Markdown

Hi,

Sebastian Bergmann wrote:

Is there another solution to this problem (apart from explicitly
unsetting the $children array on the $parent object)?And even if there
is I think that this method would be usefull.

You could use references, you would have to move some code around, though.
I'm not sure that's exactly what you want, but give it a shot:

class ParentC {
public $children = array();

   public function __construct() {
       print "ParentC::__construct()\n";
   }

   public function __destruct() {
       print "ParentC::__destruct()\n";
   }

}

class Child {
public $parentO = null;

   public function __construct() {
       print "Child::__construct()\n";
   }

   public function __destruct() {
       print "Child::__destruct()\n";
   }

}

function &setup() {
$parent = new ParentC;
$child = new Child;
$parent->children[] = &$child;
$child->parentO = &$parent;
return $parent;
}

$parent = &setup();
$parent = null;

echo "--end--\n";

Result:

ParentC::__construct()
Child::__construct()
ParentC::__destruct()
Child::__destruct()
--end--

--
Etienne Kneuss
http://www.colder.ch
colder@php.net

Men never do evil so completely and cheerfully as
when they do it from a religious conviction.
-- Pascal

A possible solution to this problem would be the introduction of yet
another "magic" method. This method would be automatically called when
unset() is called on an object that implements it. Unfortunately, the
name __unset() is already taken.

Is there another solution to this problem (apart from explicitly
unsetting the $children array on the $parent object)?And even if there
is I think that this method would be usefull.

To do this >right< you'd need notification, not just that unset() was
called on the object, but what the current state of both of its
relevant reference counts are.

class foo {
public function __delref($objectstore_refcount, $zval_refcount)
{
if ($objectstore_refcount == 1) {
/* Only one zval is pointing to this object,
* e.g. the one used/shared by the child's backreference */

   if ($zval_refcount == 1) {
     /* Only one variable is pointing to this zval,
      * the child's backreference property */
     $this->children = array();
   }
 }

}
}

Of course, that assumes you only have one child. Once you introduce
multiple children, they'll *probably share one object store reference
through a common zval with multiple references, so you could do:

class foo {
public function __delref($objectstore_refcount, $zval_refcount)
{
if ($objectstore_refcount == 1) {
/* Only one zval is pointing to this object,
* e.g. the one used/shared by the child's backreference */

   if ($zval_refcount == count($this->children)) {
     /* Only one children's properties are pointing to this zval */
     $this->children = array();
   }
 }

}
}

But that doesn't cover the (quite common) case where there are multiple
object store references spread out among the children (and possibly
other variables not contained in the object itself). Unfortunately you
can't aggregate the total number of variable->zval->object references
ince at this point in runtime, only the zval being dereferenced is known
for certain.

By the way, this is part of the reason why PHP doesn't have delete().

-Sara