Add support for readonly classes

[kocsismate]

RFC: https://wiki.php.net/rfc/readonly_classes

[nikic]

Looks reasonable to me.

[kocsismate]

@nikic Do you have any suggestion regarding static properties? I'm unsure if readonly classes should be forbidden to declare them or they should be allowed?

[nikic]

@kocsismate I'd say forbidden. In the future, we may want to support readonly static properties in the future (they mainly weren't originally included for technical reasons -- too much effort for little practical use) in which case one would expect that a static property on a readonly class would also be readonly. If we allow them now though, that wouldn't be the case.

[kocsismate]

I'd say forbidden. In the future, we may want to support readonly static properties in the future (they mainly weren't originally included for technical reasons -- too much effort for little practical use) in which case one would expect that a static property on a readonly class would also be readonly. If we allow them now though, that wouldn't be the case

Thanks for the answer! I was also slightly towards making the rules stricter now so that the restrictions can be lifted afterwards, but wasn't exactly sure. I'll update the implementation, + the RFC, and start discussion a bit later.

[amcsi]

Is the purpose of this really just to have a shorthand for all properties being readonly, or is this meant to enable true immutable strictures? Because if it'd the latter, then perhaps it could be taken a step further and only allow for instances of readonly classes for object properties. Maybe even disallow resources, and disallow being able to create (mutable) references to properties if we want to go real strict with immutability.

[kocsismate]

Is the purpose of this really just to have a shorthand for all properties being readonly, or is this meant to enable true immutable strictures? Because if it'd the latter, then perhaps it could be taken a step further and only allow for instances of readonly classes for object properties. Maybe even disallow resources, and disallow being able to create (mutable) references to properties if we want to go real strict with immutability.

The purpose is to offer a shorthand for readonly properties. I think it's a very light and flexible way to add support for immutable-alike classes. If someone wants to make one step ahead then an immutable keyword would be the best way forward. But I see the value in a readonly class modifier as well.

Because if it'd the latter, then perhaps it could be taken a step further and only allow for instances of readonly classes for object properties.

It sounds like a good idea for me at first, but doing so would create an inconsinstency: readonly properties can be non-readonly classes, while readonly classes cannot include non-readonly class properties.

Maybe even disallow resources,

There's no resource type, so it's not feasible to do.

If you'd like to continue the discussion, please use the mailing list instead. :)

[kocsismate]

I'm going to merge this PR mid next week, unless there is any issue with the implementation.

[nikic]

Implementation looks fine.