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Date: Tue, 1 Oct 2024 13:56:26 +0200
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Subject: Re: [PHP-DEV] Protected destructors
To: Jonathan Vollebregt <jnv@jnvsor.net>
Cc: internals@lists.php.net
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From: arnaud.lb@gmail.com (Arnaud Le Blanc)

Hi Jonathan,

> It seems the protected but not private destructors idea was already
> implemented for PHP 7 (https://3v4l.org/6DFGp) but fell victim to a
> regression in 7.3.15/7.4.3 and no-one noticed because it was never added
> to the changelog in the first place.

Apparently the engine can successfully call non-public destructors
when in the right scope: https://3v4l.org/FEV2fT. This is intentional
behavior, as we have explicit visibility checks in the code that calls
destructors, and tests for this. This was implemented in the 5.0
development period at the same time as other work on magic method
visibility, so my interpretation is that it was likely done purely for
consistency. What changed in 7.3.15 is that local variables are now
destroyed _after_ popping the current stack frame, which affects the
scope in which the object is destroyed in your snippet.

This is similar to __construct() and __clone() (whose visibility is
used to restrict who can perform the related operation), except that
the visibility of __destruct() doesn't really prevent the operation
from being performed: the object is still freed after the engine
failed to call the destructor. I'm not aware of use-cases for this.
Also it would be unreliable as the timing of destructor calls is not
always obvious or predictable.

Although the current behavior doesn't seem useful, the proposed
changes would only address the problem for destructors: We can not
apply the same trick to __construct() and __clone().

Best Regards,
Arnaud