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PHP RFC: Readonly classes
- Date: 2021-08-04
- Author: Máté Kocsis kocsismate@php.net
- Status: Draft
- Target Version: PHP 8.2
- Implementation: https://github.com/php/php-src/pull/7305
Introduction
PHP 8.1 added support for readonly properties via PHP RFC: Readonly properties 2.0. However, it's still not easy to declare (quasi-)immutable classes, especially if they contain many properties. Therefore, this RFC proposes adding support for readonly
classes.
Proposal
The usage of the readonly
modifier added by PHP RFC: Readonly properties 2.0 is extended to classes:
readonly class Test { public string $prop; }
Doing so will implicitly mark all instance properties of a class as readonly. Furthermore, it will prevent the usage of dynamic properties.
Restrictions
A readonly class can only have typed properties, since untyped properties cannot be marked as readonly
.
As static properties are also not covered by the Readonly properties RFC, readonly classes cannot declare them either.
Inheritance
Similarly how overriding of readonly properties work, only a readonly class can extend a readonly parent:
class A {} readonly class B extends A {}
Both of the following are illegal:
readonly class A {} class B extends A {}
class A {} readonly class B extends A {}
Reflection
A ReflectionClass::isReadOnly()
method is added, which reports whether a class is declared as read-only. Additionally, ReflectionClass::getModifiers()
will also include the ReflectionClass::IS_READONLY
flag.
Backward Incompatible Changes
None.
Vote
Add readonly classes as proposed?