Newsgroups: php.internals
Path: news.php.net
Xref: news.php.net php.internals:122900
Precedence: bulk
MIME-Version: 1.0
References: <CAPyj-LA7kJLdz3Pzbxr6x-7v2YV8n06pwxs6QoVe3CGgx-_GGA@mail.gmail.com>
 <9aeebf8e-d6a3-4d55-a926-77433a0bf4e2@gmail.com>
In-Reply-To: <9aeebf8e-d6a3-4d55-a926-77433a0bf4e2@gmail.com>
Date: Wed, 3 Apr 2024 00:35:34 +0200
Message-ID: <CAPyj-LCLb8vWXTeX8gCX18ZQ=w=1O1mYTV6pB0p0AVyUjcyvBw@mail.gmail.com>
Subject: Re: [PHP-DEV] [RFC][Concept] Data classes (a.k.a. structs)
To: PHP internals <internals@lists.php.net>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
From: tovilo.ilija@gmail.com (Ilija Tovilo)

Hi Niels

On Tue, Apr 2, 2024 at 8:16=E2=80=AFPM Niels Dossche <dossche.niels@gmail.c=
om> wrote:
>
> On 02/04/2024 02:17, Ilija Tovilo wrote:
> > Hi everyone!
> >
> > 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#).
>
> As already hinted in the thread, I also think inheritance may be dangerou=
s in a first version.
> I want to add to that: if you extend a data-class with a non-data-class, =
the data-class behaviour gets lost, which is logical in a sense but also su=
rprised me in a way.

Yes, that's definitely not intended. I haven't implemented any
inheritance checks yet. But if inheritance is allowed, then it should
be restricted to classes of the same kind (by-ref or by-val).

> Also, FWIW, I'm not sure about the name "data" class, perhaps "value" cla=
ss or something alike is what people may be more familiar with wrt semantic=
s, although dataclass is also a known term.

I'm happy with value class, struct, record, data class, what have you.
I'll accept whatever the majority prefers.

> I do have a question about iterator behaviour. Consider this code:
> ```
> data class Test {
>         public $a =3D 1;
>         public $b =3D 2;
> }
>
> $test =3D new Test;
> foreach ($test as $k =3D> &$v) {
>         if ($k =3D=3D=3D "b")
>                 $test->a =3D $test;
>         var_dump($k);
> }
> ```
>
> This will reset the iterator of the object on separation, so we will get =
an infinite loop.
> Is this intended?
> If so, is it because the right hand side is the original object while the=
 left hand side gets the clone?
> Is this consistent with how arrays separate?

That's a good question. I have not really thought about iterators yet.
Modification of an array iterated by-reference does not restart the
iterator. Actually, by-reference capturing of the value also captures
the array by-reference, which is not completely intuitive.

My initial gut feeling is to handle data classes the same, i.e.
capture them by-reference when iterating the value by reference, so
that iteration is not restarted.

Ilija