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Thread-Topic: [PHP-DEV] [RFC] Deprecate dynamic properties
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Date: Wed, 25 Aug 2021 14:26:12 +0000
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Subject: Re: [PHP-DEV] [RFC] Deprecate dynamic properties
From: tysonandre775@hotmail.com (tyson andre)

Hi Nikita Popov,=0A=
=0A=
> I'd like to propose the deprecation of "dynamic properties", that is=0A=
> properties that have not been declared in the class (stdClass and=0A=
> __get/__set excluded, of course):=0A=
> =0A=
> https://wiki.php.net/rfc/deprecate_dynamic_properties=0A=
> =0A=
> This has been discussed in various forms in the past, e.g. in=0A=
> https://wiki.php.net/rfc/locked-classes as a class modifier and=0A=
> https://wiki.php.net/rfc/namespace_scoped_declares /=0A=
> https://github.com/nikic/php-rfcs/blob/language-evolution/rfcs/0000-langu=
age-evolution.md=0A=
> as a declare directive.=0A=
> =0A=
> This RFC takes the more direct route of deprecating this functionality=0A=
> entirely. I expect that this will have relatively little impact on modern=
=0A=
> code (e.g. in Symfony I could fix the vast majority of deprecation warnin=
gs=0A=
> with a three-line diff), but may have a big impact on legacy code that=0A=
> doesn't declare properties at all.=0A=
=0A=
I'd had some concerns.=0A=
=0A=
It might be too soon after your addition of WeakMap.=0A=
https://www.php.net/weakmap was introduced in PHP 8.0 (and WeakReference in=
 7.4),=0A=
so applications/libraries fixing the deprecation may need to drop support f=
or php 7.x early.=0A=
Applications attempting to polyfill a WeakMap in earlier PHP versions would=
 potentially leak a lot of memory in php 7.x.=0A=
=0A=
- I don't know how many minor versions to expect before 9.0 is out=0A=
- Is it feasible for a developer to create a native PECL polyfill for WeakM=
ap for earlier PHP versions that has a=0A=
  subset of the functionality the native weak reference counting does?=0A=
  (e.g. to only free polyfilled weak references when cyclic garbage collect=
ion is triggered and the reference count is 1).=0A=
=0A=
Additionally, it makes it less efficient (but still feasible) to associate =
additional fields=0A=
with libraries or native classes/PECLs you don't own (especially for circul=
ar data structures), especially if they need to be serialized later.=0A=
(it isn't possible to serialize WeakMap, and the WeakMap would have fields =
unrelated to the data being serialized)=0A=
I guess you can have a wrapper class that iterates over a WeakMap to captur=
e and serialize the values that still exist in SplObjectStorage, though.=0A=
(Though other languages do just fine without this functionality)=0A=
=0A=
I'm not sure if a library owner would want to change their class hierarchy =
to extend stdClass (to avoid changing the behavior of anything using `$x in=
stanceof stdClass`) and the attribute/trait approach might be more acceptab=
le to library owners.=0A=
E.g. https://github.com/vimeo/psalm/blob/master/src/Psalm/Internal/Analyzer=
/Statements/Expression/Call/FunctionCallAnalyzer.php =0A=
would set a dynamic property `$stmt->pure` in `PhpParser\Node\Expr\FuncCall=
 $stmt` in a vendor dependency on php-parser.=0A=
=0A=
Regards,=0A=
Tyson=0A=