make new return a reference to existent object View as Markdown

That is perfect Duncan, that was my first impression, but I think i read that
there was something to adding new magic methods, however, i think that would
be the perfect solution.

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 implemented
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=array();

  public static function loadObject($class, $id) {
  if(isset(ObjectStore::instances[$class][$id])) {
  ObjectStore::instances[$class][$id][1]++;
  return ObjectStore::instances[$class][$id][0];
  }

  $handle = SomeDatabaseClass::getHandle();
  $result = $handle->query("SELECT * FROM $class WHERE id=$id");
  if(!$result->num_rows()) {
  	throw new Exception("Object $class $id does not exist in the database");
  }
  $r = $result->fetch_object();
  $obj = new $class();
  $obj->deserialize($r);
  ObjectStore::instances[$class][$id]=array($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=true;
  }
  return $this;
  }

  /**

  • Retrieve the object's properties from a database row
    **/
    abstract public function deserialize($db_object);
    }

Then load objects by calling

$obj = ObjectStore::loadObject("SomeClass",27);
And when you're done with them call unset($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

--

Leonardo Pedretti
Axon Sistemas
Líder de Equipo Proyecto Basalto