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

PHP 8.1 added support for readonly properties via PHP RFC: Readonly properties 2.0.

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 typed instance properties of a class as readonly. Furthermore, it will prevent the usage of dynmacic properties.

A readonly class can only have typed properties.

Readonly static properties are not supported. This is a technical limitation, in that it is not possible to implement readonly static properties non-intrusively. In conjunction with the questionable usefulness of readonly static properties, this is not considered worthwhile at this time.

Similarly how overriding of readonly properties work, only a readonly class can extend a readonly class:

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 {}

A ReflectionClass::isReadOnly() method is added, which reports whether a class is declared as read-only. ReflectionClass::getModifiers() will also report a ReflectionClass::IS_READONLY flag.

None.

Add readonly classes as proposed?