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Date: Tue, 2 Apr 2024 11:24:42 +0200
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Subject: Re: [PHP-DEV] [RFC][Concept] Data classes (a.k.a. structs)
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From: tovilo.ilija@gmail.com (Ilija Tovilo)

Hi Alexander

On Tue, Apr 2, 2024 at 4:53=E2=80=AFAM Alexander Pravdin <alex.pravdin@inte=
ri.co> wrote:
>
> On Tue, Apr 2, 2024 at 9:18=E2=80=AFAM Ilija Tovilo <tovilo.ilija@gmail.c=
om> wrote:
> >
> > I'd like to introduce an idea I've played around with for a couple of
> > weeks: Data classes, sometimes called structs in other languages (e.g.
> > Swift and C#).
>
> While I like the idea, I would like to suggest something else in
> addition or as a separate feature. As an active user of readonly
> classes with all promoted properties for data-holding purposes, I
> would be happy to see the possibility of cloning them with passing
> some properties to modify:
>
> readonly class Data {
>     function __construct(
>         public string $foo,
>         public string $bar,
>         public string $baz,
> ) {}
> }
>
> $data =3D new Data(foo: 'A', bar: 'B', baz: 'C');
>
> $data2 =3D clone $data with (bar: 'X', baz: 'Y');

What you're asking for is part of the "Clone with" RFC:
https://wiki.php.net/rfc/clone_with

This issue is valid and the RFC would improve the ergonomics of
readonly classes.

However, note that it really only addresses a small part of what this
RFC tries achieve:

> Some APIs further exacerbate the issue by
requiring multiple copies for multiple modifications (e.g.
`$response->withStatus(200)->withHeader('X-foo', 'foo');`).

Readonly works fine for compact data structures, even if it is copied
more than it needs. For large data structures, like large lists, a
copy for each modification would be detrimental.

https://3v4l.org/GR6On

See how the performance of an insert into an array tanks if a copy of
the array is performed in each iteration (due to an additional
reference to it). Readonly is just not viable for data structures such
as lists, maps, sets, etc.

Ilija