Implement WeakMap

[nikic]

Implementation for https://wiki.php.net/rfc/weak_maps.

[ntzm]

I really like this, really like this. However, is there any chance of removing the limit of only allowing objects as keys? I would like to be able to do something like:

$map = new WeakMap();

$map[5] = 'foo';

$foo = new stdClass();
$map[$foo] = 'bar';

[nikic]

@ntzm What use case do you have in mind for mixing object and non-object keys in the weak map?

Supporting this is going to make the implementation a lot more complex (right now objects are stored as integers, so we can't easily support other integer keys), and it seems like a semantically pretty odd thing to do to me. The "weak" part of the map only applies to objects, so also allowing other key types with non-weak semantics seems odd/misleading.

[ntzm]

My case is something like this:

I have a decorator class that caches the result of method calls, and the method argument takes any type.

At the moment it works by serialising and hashing the argument, and using that as an array key. This is to avoid adding a reference to the object with SplObjectStorage.

I can understand your reasoning completely, I think the best solution for my problem is to use WeakMap for objects, and a standard array map for scalar types.

Thanks!

[mvorisek]

It would be great if the WeakMap would allow to define a callback which will be invoked before the key/value is garbage collected. The same for WeakMap. It would then allow "a lots of magic" for caches etc.

[nikic]

@mvorisek It's possible to store an object with a destructor inside the weak map, which will effectively result in such a callback. A dummy example:

$object = new stdClass;
$map = new WeakMap;
$map[$object] = new class {
    public function __destruct() {
        echo "Object destroyed!\n";
    }
};
unset($object);

This is of course somewhat roundabout.

[mvorisek]

This is of course somewhat roundabout.

You are right and I think this is enought for now.

[nikic]

RFC accepted. Merged as d8c9902.

[mvorisek]

@nikic wdyt about doctrine/orm#7998 (comment) , is there currently any option to register for destruct event and possibility to cancel it? It seems like needed if the target object does not / can not implement a custom __destruct method.