Generic php4 method to get a singleton
Quickly, a generic method to get a singleton in php4. Juste paste this method in your class definition :
function & getSingleton() {
$class=--CLASS--; // getting current class name
// need to build singleton ?
if (!isset($GLOBALS['singletons'][$class])) {
// getting arguments to forward
$args=func_get_args();
/* building instanciation code, forwarding arguments
creating singleton and a single global reference per class name */
$eval='$GLOBALS[\'singletons\'][$class]=& new $class(';
// adding arguments to constructor
for ($f=0; $f<count($args); $f++) $eval.='$args['.$f.'],';
// deleting last unnecessary ',' and closing call
$eval=substr($eval,0,-1).');';
// executing instanciation code
eval($eval);
}
// throwing instance
return $GLOBALS['singletons'][$class];
}
So you can get a single instance of your class with a static call of getSingleton, like your_class::getsingleton($arg1, $arg2,...);. You can edventually add an alert in the class constructor like this :
function the_class_constructor_method() {
if (isset($GLOBALS['singletons'][__CLASS__])) {
trigger_error("Use ".__CLASS__."::getSingleton(); to get a single instance of ".__CLASS__);
}
}
Please note that this isn't the clean, righteous way to implement Singleton pattern : because in php4 it seems not possible to have the class constructor returning anything else than a new instance of the class, nor to make the constructor private. Therefore it is still possible to have multiple instances of the class, by calling its constructor directly.
jabber
