Re: Possible RFC: UniqueInterface that throws exception at refcount > 1

2020-07-11 14:55 GMT, tyson andre <tysonandre775@hotmail.com>: >> Yes, it would be a dynamic uniqueness system, kind of. >> >> Another more flexible alternative would be to add magic methods at >> refcount = 1 and refcount > 1, possibly __owned() and __shared(int >> $refcount), for classes that implement a TrackReferencesInterface or >> similar. But this would need to do ~0 performance hit if not used, >> don't know if possible. > > Then again, php already calls __destruct if it exists when the refcount goes > to 0, > so I may be overestimating the potential performance impact. > > There's a lot of edge cases - probably way more than I mention here. > Running into those edge cases, you might find the feature unsatisfactory if > it were to be implemented. > > For example, > - The UniqueReferenceException itself creates a trace, that increments > reference counts, which might itself cause a UniqueReferenceException. > Workarounds for that would probably involve allowing multiple objects to > reference a UniqueInterface, and then it would be a weaker guarantee. > - unserialize() keeps extra references to ensure that it can delete the > created objects if the original references were overwritten. __wakeup() and > __unserialize() > - The reference count is incremented when calling __destruct(), I think. > > ``` > <?php > class UniqueObject implements UniqueInterface{ > public function __construct() { > debug_zval_dump($this); // refcount 3 - and then what about > $GLOBALS['something'] = $this inside __construct > } > public function someUtilMethod() { > // object(UniqueObject)#1 (0) refcount(2){ > // } > debug_zval_dump($this); > } > } > // The reference count goes to 2 in someUtilMethod because there's 2 > references. > // the temporary and $this. > (new UniqueObject())->someUtilMethod(); > ``` > > - Tyson All good points. It's better to have a magic method that catches changes in the refcount instead, just like __destruct but on any change, not only at zero. Olle