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Date: Sat, 23 Nov 2024 17:02:52 +0200
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Subject: Re: [PHP-DEV] [RFC] Data Classes
To: Rob Landers <rob@bottled.codes>
Cc: internals@lists.php.net
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From: zsidelnik@gmail.com (Eugene Sidelnyk)

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Hello

If I remember correctly, the whole concept of "value" is fully described in
DDD book by Eric Evans. If that's the point of the RFC, I wonder of there's
any point in not making such classes immutable by default, and to keep only
one instance of value object unique per given set of properties in memory,
thereby eliminating cloning altogether and optimizing the memory usage.

On Sat, Nov 23, 2024, 3:12 PM Rob Landers <rob@bottled.codes> wrote:

> Hello internals,
>
> Born from the Records RFC (https://wiki.php.net/rfc/records) discussion,
> I would like to introduce to you a competing RFC: Data Classes (
> https://wiki.php.net/rfc/dataclass).
>
> This adds a new class modifier: data. This modifier drastically changes
> how classes work, making them comparable by value instead of reference, a=
nd
> any mutations behave more like arrays than objects (by vale). If desired,
> it can be combined with other modifiers, such as readonly, to enforce
> immutability.
>
> I've been playing with this feature for a few days now, and it is
> surprisingly intuitive to use. There is a (mostly) working implementation
> available on GitHub (https://github.com/php/php-src/pull/16904) if you
> want to have a go at it.
>
> Example:
>
> data class UserId { public function __construct(public int $id) {} }
>
> $user =3D new UserId(12);
> // later
> $admin =3D new UserId(12);
> if ($admin =3D=3D=3D $user) { // do something } // true
>
> Data classes are true value objects, with full copy-on-write optimization=
s:
>
> data class Point {
>   public function __construct(public int $x, public int $y) {}
>   public function add(Point $other): Point {
>     // illustrating value semantics, no copy yet
>     $previous =3D $this;
>     // a copy happens on the next line
>     $this->x =3D $this->x + $other->x;
>     $this->y =3D $this->y + $other->y;
>     assert($this !=3D=3D $previous); // passes
>     return $this;
>   }
> }
>
> I think this would be an amazing addition to PHP.
>
> Sincerely,
>
> =E2=80=94 Rob
>

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<p dir=3D"ltr">Hello</p>
<p dir=3D"ltr">If I remember correctly, the whole concept of &quot;value&qu=
ot; is fully described in DDD book by Eric Evans. If that&#39;s the point o=
f the RFC, I wonder of there&#39;s any point in not making such classes imm=
utable by default, and to keep only one instance of value object unique per=
 given set of properties in memory, thereby eliminating cloning altogether =
and optimizing the memory usage.</p>
<br><div class=3D"gmail_quote"><div dir=3D"ltr" class=3D"gmail_attr">On Sat=
, Nov 23, 2024, 3:12 PM Rob Landers &lt;rob@bottled.codes&gt; wrote:<br></d=
iv><blockquote class=3D"gmail_quote" style=3D"margin:0 0 0 .8ex;border-left=
:1px #ccc solid;padding-left:1ex"><u></u><div><div>Hello internals,<br></di=
v><div><br></div><div>Born from the Records RFC (<a href=3D"https://wiki.ph=
p.net/rfc/records" target=3D"_blank" rel=3D"noreferrer">https://wiki.php.ne=
t/rfc/records</a>) discussion, I would like to introduce to you a competing=
 RFC: Data Classes (<a href=3D"https://wiki.php.net/rfc/dataclass" target=
=3D"_blank" rel=3D"noreferrer">https://wiki.php.net/rfc/dataclass</a>).=C2=
=A0<br></div><div><br></div><div>This adds a new class modifier: data. This=
 modifier drastically changes how classes work, making them comparable by v=
alue instead of reference, and any mutations behave more like arrays than o=
bjects (by vale). If desired, it can be combined with other modifiers, such=
 as readonly, to enforce immutability.<br></div><div><br></div><div>I&#39;v=
e been playing with this feature for a few days now, and it is surprisingly=
 intuitive to use. There is a (mostly) working implementation available on =
GitHub (<a href=3D"https://github.com/php/php-src/pull/16904" target=3D"_bl=
ank" rel=3D"noreferrer">https://github.com/php/php-src/pull/16904</a>) if y=
ou want to have a go at it.<br></div><div><br></div><div>Example:<br></div>=
<div><br></div><div>data class UserId { public function __construct(public =
int $id) {} }<br></div><div><br></div><div>$user =3D new UserId(12);<br></d=
iv><div>// later<br></div><div>$admin =3D new UserId(12);<br></div><div>if =
($admin =3D=3D=3D $user) { // do something } // true<br></div><div><br></di=
v><div>Data classes are true value objects, with full copy-on-write optimiz=
ations:<br></div><div><br></div><div>data class Point {<br></div><div>=C2=
=A0 public function __construct(public int $x, public int $y) {}<br></div><=
div>=C2=A0 public function add(Point $other): Point {<br></div><div>=C2=A0 =
=C2=A0 // illustrating value semantics, no copy yet<br></div><div>=C2=A0 =
=C2=A0 $previous =3D $this;<br></div><div>=C2=A0 =C2=A0 // a copy happens o=
n the next line<br></div><div>=C2=A0 =C2=A0 $this-&gt;x =3D $this-&gt;x + $=
other-&gt;x;<br></div><div>=C2=A0 =C2=A0 $this-&gt;y =3D $this-&gt;y + $oth=
er-&gt;y;<br></div><div>=C2=A0 =C2=A0 assert($this !=3D=3D $previous); // p=
asses<br></div><div>=C2=A0 =C2=A0 return $this;<br></div><div>=C2=A0 }<br><=
/div><div>}<br></div><div><br></div><div>I think this would be an amazing a=
ddition to PHP.=C2=A0<br></div><div><br></div><div>Sincerely,</div><div><br=
></div><div id=3D"m_-3199207564271075714sig121229152">=E2=80=94 Rob<br></di=
v></div></blockquote></div>

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