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PHP RFC: Final anonymous classes
- Date: 2023-11-15
- Author: Daniil Gentili daniil@daniil.it
- Status: Under Discussion
Introduction
This RFC proposes to add support for final anonymous classes, or make all anonymous classes final by default, with or without the possibility to make them non-final.
Proposal
This RFC proposes to either add support for final anonymous classes, or make all anonymous classes final by default, with or without the possibility to make them non-final.
This should also allow some additional opcache optimizations, such as any JIT logic gated behind a check on ZEND_ACC_FINAL, i.e. https://github.com/php/php-src/blob/master/ext/opcache/jit/zend_jit_trace.c#L4507.
Personally, I would have instead preferred the much cleaner approach of making all anonymous classes final by default, (preferrably) without offering the option to make them non-final.
However, I understand that this might be a little bit too restrictive for something that may have some valid usecases, even if extending anonymous classes currently requires some hack-ish workarounds with class_alias.
Thus, this RFC includes three mutually exclusive proposals:
- Add support for final anonymous classes (new final class {} syntax, no breaking changes)
- OR Make all anonymous classes final by default, without the option to make them final (breaking change)
- OR Make all anonymous classes final by default, provide an optional open keyword to make them non-final (like in Kotlin, new open class {}, no breaking changes).
As an extra proposal related to the last two options, possibly requiring a separate RFC, in the last two cases, it might be a good idea to also disallow the use of class_alias altogether for final anonymous classes (suggested by nikolas-grekas in https://github.com/php/php-src/pull/11126#issuecomment-1522042841).
Backward Incompatible Changes
In case proposal 2 is accepted, it will break existing code which extends from anonymous classes using class_alias.
In case proposal 2 is accepted and class_alias is disallowed for final anonymous classes, it will break existing code that uses class_alias to give a name to anonymous classes, not necessarily to extend them.
Proposed PHP Version(s)
Next PHP 8.4
RFC Impact
See Backward Incompatible Changes.
Future Scope
As an extra proposal related to the last two options, possibly requiring a separate RFC, in the last two cases, it might be a good idea to also disallow the use of class_alias altogether for final anonymous classes (suggested by nikolas-grekas in https://github.com/php/php-src/pull/11126#issuecomment-1522042841).
Proposed Voting Choices
2/3 required to accept.
2/3 required to accept.
2/3 required to accept.
Patches and Tests
Final anonymous classes implementation: https://github.com/php/php-src/pull/11126
References
Pull request discussion: https://github.com/php/php-src/pull/11126 Internals discussion: https://externals.io/message/121356