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Date: Sat, 23 Nov 2024 14:11:56 +0100
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Subject: [PHP-DEV] [RFC] Data Classes
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From: rob@bottled.codes ("Rob Landers")

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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).=20

This adds a new class modifier: data. This modifier drastically changes =
how classes work, making them comparable by value instead of reference, =
and any mutations behave more like arrays than objects (by vale). If des=
ired, it can be combined with other modifiers, such as readonly, to enfo=
rce immutability.

I've been playing with this feature for a few days now, and it is surpri=
singly intuitive to use. There is a (mostly) working implementation avai=
lable 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 optimizatio=
ns:

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.=20

Sincerely,

=E2=80=94 Rob
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<!DOCTYPE html><html><head><title></title><style type=3D"text/css">p.Mso=
Normal,p.MsoNoSpacing{margin:0}=0Ap.MsoNormal,p.MsoNoSpacing{margin:0}</=
style></head><body><div>Hello internals,<br></div><div><br></div><div>Bo=
rn from the Records RFC (<a href=3D"https://wiki.php.net/rfc/records">ht=
tps://wiki.php.net/rfc/records</a>) discussion, I would like to introduc=
e to you a competing RFC: Data Classes (<a href=3D"https://wiki.php.net/=
rfc/dataclass">https://wiki.php.net/rfc/dataclass</a>).&nbsp;<br></div><=
div><br></div><div>This adds a new class modifier: data. This modifier d=
rastically changes how classes work, making them comparable by value ins=
tead of reference, and any mutations behave more like arrays than object=
s (by vale). If desired, it can be combined with other modifiers, such a=
s readonly, to enforce immutability.<br></div><div><br></div><div>I've b=
een 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">https:/=
/github.com/php/php-src/pull/16904</a>) if you 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></div><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></div><div>Data cl=
asses are true value objects, with full copy-on-write optimizations:<br>=
</div><div><br></div><div>data class Point {<br></div><div>&nbsp; public=
 function __construct(public int $x, public int $y) {}<br></div><div>&nb=
sp; public function add(Point $other): Point {<br></div><div>&nbsp; &nbs=
p; // illustrating value semantics, no copy yet<br></div><div>&nbsp; &nb=
sp; $previous =3D $this;<br></div><div>&nbsp; &nbsp; // a copy happens o=
n the next line<br></div><div>&nbsp; &nbsp; $this-&gt;x =3D $this-&gt;x =
+ $other-&gt;x;<br></div><div>&nbsp; &nbsp; $this-&gt;y =3D $this-&gt;y =
+ $other-&gt;y;<br></div><div>&nbsp; &nbsp; assert($this !=3D=3D $previo=
us); // passes<br></div><div>&nbsp; &nbsp; return $this;<br></div><div>&=
nbsp; }<br></div><div>}<br></div><div><br></div><div>I think this would =
be an amazing addition to PHP.&nbsp;<br></div><div><br></div><div>Sincer=
ely,</div><div><br></div><div id=3D"sig121229152">=E2=80=94 Rob<br></div=
></body></html>
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