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Date: Tue, 24 Feb 2026 19:50:37 +0000
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Subject: Re: [PHP-DEV] [RFC] Readonly Variables
To: Larry Garfield <larry@garfieldtech.com>
Cc: php internals <internals@lists.php.net>
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From: tekiela246@gmail.com (Kamil Tekiela)

On Tue, 24 Feb 2026 at 19:32, Larry Garfield <larry@garfieldtech.com> wrote=
:
>
> On Tue, Feb 24, 2026, at 12:52 PM, Joshua R=C3=BCsweg wrote:
>
> >> I would prefer starting with readonly parameters as I feel that would
> >> bring the most value.
> >
> > I find the idea of readonly parameters interesting and have already
> > given it some thought. However, it is out of scope for this RFC, as I
> > wanted to keep the initial proposal focused and manageable. I have
> > already mentioned it in the Future Scope section of the RFC as a
> > potential natural extension that could be addressed in a separate RFC
> > in the future.
>
> A slight tangent here, but what would readonly parameters do?
>
> If you pass something by value, then already you cannot modify the value =
in the caller.  If the value is large, it's already kept efficient by copy-=
on-write.
>
> If you pass by reference, then presumably you *want* to modify the value =
in the caller.
>
> If the value is an object, then as already discussed, its internals are m=
utable either way so you gain little, but the function cannot change the id=
entity in the caller anyway.
>
> So I don't see what readonly parameters would even accomplish.  The thing=
 they accomplish in JS or Java or C simply doesn't apply in PHP.
>
> I'm still undecided at the moment on readonly variables.
>
> --Larry Garfield

A readonly parameter would mean that it would be impossible to reuse
the variable within the function for something else. It's not uncommon
for a function to preprocess the argument and still make use of the
original value. A readonly modifier would prevent accidental
overwrite.

function foo(string|array $data) {
    if (is_string($data) ) {
        $data =3D [$data]; // Original argument lost
    }
    // ....
    return is_string($data) ? $result : [$result];
)