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Date: Thu, 10 Jul 2025 12:43:45 +0200
To: Nicolas Grekas <nicolas.grekas+php@gmail.com>
Cc: Larry Garfield <larry@garfieldtech.com>, php internals
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Subject: Re: [PHP-DEV] [RFC] Readonly property hooks
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From: tim@bastelstu.be (=?UTF-8?Q?Tim_D=C3=BCsterhus?=)

Hi

Am 2025-07-08 17:32, schrieb Nicolas Grekas:
> I also read Tim's argument that new features could be stricter. If one
> wants to be stricter and forbid extra behaviors that could be added by
> either the proposed hooks or __get, then the answer is : make the class
> final. This is the only real way to enforce readonly-ness in PHP.

Making the class final still would not allow to optimize based on the 
fact that the identity of a value stored in a readonly property will not 
change after successfully reading from the property once. Whether or not 
a property hooked must be considered an implementation detail, since a 
main point of the property hooks RFC was that hooks can be added and 
removed without breaking compatibility for the user of the API.

> engine-assisted strictness in this case. You cannot write such code in 
> a
> non-readonly way by mistake, so it has to be by intent.

That is saying "it's impossible to introduce bugs".

> PS: as I keep repeating, readonly doesn't immutable at all. I know this 
> is
> written as such in the original RFC, but the concrete definition and
> implementation of readonly isn't: you can set mutable objects to 
> readonly
> properties, and that means even readonly classes/properties are 
> mutable, in
> the generic case.

`readonly` guarantees the immutability of identity. While you can 
certainly mutate mutable objects, the identity of the stored object 
doesn't change.

Best regards
Tim Düsterhus