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Date: Thu, 10 Jul 2025 10:34:15 -0500
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Subject: Re: [PHP-DEV] [RFC] Readonly property hooks
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From: larry@garfieldtech.com ("Larry Garfield")

On Thu, Jul 10, 2025, at 5:43 AM, Tim D=C3=BCsterhus wrote:
> 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 cla=
ss
>> 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=20
> fact that the identity of a value stored in a readonly property will n=
ot=20
> change after successfully reading from the property once. Whether or n=
ot=20
> a property hooked must be considered an implementation detail, since a=20
> main point of the property hooks RFC was that hooks can be added and=20
> removed without breaking compatibility for the user of the API.
>
>> engine-assisted strictness in this case. You cannot write such code i=
n=20
>> 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 th=
is=20
>> is
>> written as such in the original RFC, but the concrete definition and
>> implementation of readonly isn't: you can set mutable objects to=20
>> readonly
>> properties, and that means even readonly classes/properties are=20
>> mutable, in
>> the generic case.
>
> `readonly` guarantees the immutability of identity. While you can=20
> certainly mutate mutable objects, the identity of the stored object=20
> doesn't change.
>
> Best regards
> Tim D=C3=BCsterhus

Nick previously suggested having the get-hook's first return value cache=
d; it would still be subsequently called, so any side effects would stil=
l happen (though I don't know why you'd want side effects), but only the=
 first returned value would ever get returned.  Would anyone find that a=
cceptable?  (In the typical case, it would be the same as the current $t=
his->foo ??=3D compute() pattern, just with an extra cache entry.)

--Larry Garfield