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Date: Wed, 11 May 2005 12:48:45 -0300
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Subject: [PHP-DEV] magic detecting reference deletion
From: lpedretti@suserver.com (Leonardo Pedretti)

That is perfect Duncan, that was my first impression, but I think i read th=
at=20
there was something to adding new magic methods, however, i think that woul=
d=20
be the perfect solution.

On Wednesday 11 May 2005 06:14, Duncan McIntyre wrote:
> Wez,
>
> I have similar problems. I think your suggested solution is the wrong
> approach because your problem is not creating objects, it is destroying
> them.
>
> My solution would be to define a new magic static method __free() which is
> given an instance of the class every time a reference to that instance is
> deleted. This would be a hook into the code which calls __destruct() once
> an object's ref count reaches zero, except that it would call __free()
> every time an object's ref count was decremented.
>
> class SomeClass {
>  public static __free($instance) {
>   /**
>   * Do some static instance caching magic here
>   **/
>  }
> }
>
> This would be a neat addition to the language, but unless it is implement=
ed
> you will have to use a bit of discipline in writing your code instead.
>
> The example below is probably the best you can do:
>
> /**
> * This class provides the mechanism to load objects from the database
> * and caches loaded instances
> **/
> class ObjectStore {
>
> 	static $instances=3Darray();
>
> 	public static function loadObject($class, $id) {
> 		if(isset(ObjectStore::instances[$class][$id])) {
> 			ObjectStore::instances[$class][$id][1]++;
> 			return ObjectStore::instances[$class][$id][0];
> 		}
>
> 		$handle =3D SomeDatabaseClass::getHandle();
> 		$result =3D $handle->query("SELECT * FROM $class WHERE id=3D$id");
> 		if(!$result->num_rows()) {
> 			throw new Exception("Object $class $id does not exist in the database"=
);
> 		}
> 		$r =3D $result->fetch_object();
> 		$obj =3D new $class();
> 		$obj->deserialize($r);
> 		ObjectStore::instances[$class][$id]=3Darray($obj, 1);
> 		return $obj;
> 	}
>
> 	public static function free($obj) {
> 		ObjectStore::instances[$obj->class][$obj->id][1]--;
> 		if(!ObjectStore::instances[$obj->class][$obj->id][1]) {
> 			unset(ObjectStore::instances[$obj->class][$obj->id]);
> 		}
> 	}
> }
>
> /**
> * All classes stored in the database must extend this class
> **/
> abstract class PersistentObject {
> 	public function free() {
> 		static $freed;
> 		if(!$freed) {
> 			ObjectStore::free($this);
> 			$freed=3Dtrue;
> 		}
> 		return $this;
> 	}
>
> 	/**
> 	* Retrieve the object's properties from a database row
> 	**/
> 	abstract public function deserialize($db_object);
> }
>
> Then load objects by calling
>
> $obj =3D ObjectStore::loadObject("SomeClass",27);
> And when you're done with them call unset($obj->free());
>
> Any classes which consume PersistentObjects must have a method __destruct=
()
> which calls free() on any PersistentObjects they have references to in
> order for this to work.
>
> Duncan

=2D-=20

Leonardo Pedretti
Axon Sistemas
L=EDder de Equipo Proyecto Basalto