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Date: Fri, 21 Jan 2022 10:31:28 +0000
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To: PHP internals <internals@lists.php.net>
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Subject: Weak Closures
From: codekestrel@googlemail.com (Dominic Grostate)

Hi Internals,

I'd like to express my interest in a possible feature concerning weak
references. Currently closures created within a class appear to
contain a reference to the object that created it. This is of course
necessary in order for the closure to retain the necessary scope.
However I would like to suggest we have the option for closure to
weakly reference this object so that when the object is garbage
collected, the closure too may be rendered null or invalid
(inspectable).

Consider the following example:
https://gist.github.com/orolyn/7651e4127759aad1736547490baa1394

The idea here is that without unset($sample) the loop would run
forever, because there is a reference to the callback from the object,
and in turn there is a reference to the object from the main stack.
With the unset($sample), the idea is that before the callback is even
called, the reference to the object is destroyed thusly so is the
reference to callback, and since the callback is only referenced now
in a WeakMap, the callback will finally be gone.

In reality it appears there is a circular reference between the object
and the callback. I don't know if this is a bug or not, because from
what I can find PHP was fixed a long time ago to resolve circular
references.

However if this is intentional, I would like the option to make the
closure weak for example:

$c = WeakClosure::fromCallable(function () {});
$c = Closure::fromCallable(function () {}, true);

Please let me know your thoughts, because maybe there is a way of
achieving this with PHP as is.

Kind regards,
Dominic