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Date: Sun, 18 Apr 2021 16:19:55 +0200
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To: PHP Internals List <internals@lists.php.net>
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Subject: [RFC] [Draft] Final constants
From: kocsismate90@gmail.com (=?UTF-8?B?TcOhdMOpIEtvY3Npcw==?=)

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Hi Internals,

I've recently realized that class constant values cannot always be trusted
when late static binding is involved (e.g. static::FOO or $this::FOO),
since they can be freely overridden in child classes. That's why the engine
knows neither the type and the value before run-time.

Doctrine coding standards has a specific rule which disallows referencing a
possibly overridden class constant (
https://github.com/doctrine/coding-standard/blob/8d75920bb04a9be4c73c2a775e=
e5766262cf2a0d/lib/Doctrine/ruleset.xml#L123
),
but I'm wondering if it would be better to simply make it possible to allow
declaring class constants final  (thus disallowing overriding) instead?

In my opinion, final constants would come with two advantages:
- make class constant declarations paranoidly safe
- allow the engine to optimize class constants references in LSB context

Although I admit that the win is not extra huge, I do think that it would
still be useful to have this feature, especially considering that the
implementation is very straightforward (
https://github.com/php/php-src/pull/6878). So that's why I'm proposing this
as an RFC.

Recently, a similar attempt to make class constant declarations safer was
the Typed Constants RFC (https://externals.io/message/110755#110755), but
unfortunately it has halted since then. I think final and typed constants
would be a nice little addition, and would complement each other well.

Regards,
M=C3=A1t=C3=A9

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