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Date: Thu, 06 Mar 2025 00:11:22 +0100
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Subject: [PHP-DEV] RFC: short and inner classes
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From: rob@bottled.codes ("Rob Landers")

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Hello PHP Internals,

I'd like to introduce my RFC for discussion: https://wiki.php.net/rfc/sh=
ort-and-inner-classes

This RFC defines a short class syntax as well as the ability to nest cla=
sses inside another class. This introduces an unprecedented amount of co=
ntrol, flexibility, and expressiveness over how objects are used and ins=
tantiated in PHP. There is a PR (https://github.com/php/php-src/pull/178=
95) that implements this functionality -- all test failures are related =
to different/new/incorrect error messages being generated. However, the =
core functionality exists to take for a test ride.

So, what do I mean by "unprecedented amount of control"? With this chang=
e, you can declare an inner class as private or protected, preventing it=
s usage outside of the outer class:

class User {
  private class Id {}

  public function __construct(public self::Id $id) {}
}

In the above example, the class `User` is impossible to construct even t=
hough it has a public constructor (except through reflection) because Us=
er::Id is private; User::Id cannot be instantiated, used as a type hint,=
 or even via `instanceof` outside of the User class itself. This example=
 isn't practical but demonstrates something that is nearly impossible in=
 previous versions of PHP, where all classes are essentially publicly ac=
cessible from anywhere within the codebase.

As a number of inner classes will probably be used as DTOs, the RFC intr=
oduces a "short syntax" for declaring classes, which enhances expressive=
ness, even allowing the usage of traits, all in a single line:

// declare a readonly Point, that implements Vector2 and uses the Evolva=
ble trait
readonly class Point(public int $x, public int $y) implements Vector2 us=
e Evolvable;

When combined with inner classes, it looks something like this:

class Pixel {
  public readonly class Point(public int $x, public int $y) implements V=
ector2 use Evolvable;
}

// Create a new pixel point with property $x and $y set to 0
$p =3D new Pixel::Point(0, 0);

There are far more details in the RFC itself, so please check it out. I'=
m quite excited to hear your thoughts!

=E2=80=94 Rob

PS. I know I tend to rush into things, but I want to make it clear that =
I'm not rushing this -- I've learned from my mistakes (thank you to thos=
e who have given me advice). I'm going to do this right.


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<!DOCTYPE html><html><head><title></title><style type=3D"text/css">p.Mso=
Normal,p.MsoNoSpacing{margin:0}</style></head><body><div>Hello PHP Inter=
nals,<br></div><div><br></div><div>I'd like to introduce my RFC for disc=
ussion:&nbsp;<a href=3D"https://wiki.php.net/rfc/short-and-inner-classes=
">https://wiki.php.net/rfc/short-and-inner-classes</a><br></div><div><br=
></div><div>This RFC defines a short class syntax as well as the ability=
 to nest classes inside another class. This introduces an unprecedented =
amount of control, flexibility, and expressiveness over how objects are =
used and instantiated in PHP. There is a PR (<a href=3D"https://github.c=
om/php/php-src/pull/17895">https://github.com/php/php-src/pull/17895</a>=
) that implements this functionality -- all test failures are related to=
 different/new/incorrect error messages being generated. However, the co=
re functionality exists to take for a test ride.<br></div><div><br></div=
><div>So, what do I mean by "unprecedented amount of control"? With this=
 change, you can declare an inner class as private or protected, prevent=
ing its usage outside of the outer class:<br></div><div><br></div><div>c=
lass User {<br></div><div>&nbsp; private class Id {}<br></div><div><br><=
/div><div>&nbsp; public function __construct(public self::Id $id) {}</di=
v><div>}<br></div><div><br></div><div>In the above example, the class `U=
ser` is impossible to construct even though it has a public constructor =
(except through reflection) because User::Id is private; User::Id cannot=
 be instantiated, used as a type hint, or even via `instanceof` outside =
of the User class itself. This example isn't practical but demonstrates =
something that is nearly impossible in previous versions of PHP, where a=
ll classes are essentially publicly accessible from anywhere within the =
codebase.<br></div><div><br></div><div>As a number of inner classes will=
 probably be used as DTOs, the RFC introduces a "short syntax" for decla=
ring classes, which enhances expressiveness, even allowing the usage of =
traits, all in a single line:<br></div><div><br></div><div>// declare a =
readonly Point, that implements Vector2 and uses the Evolvable trait</di=
v><div>readonly class Point(public int $x, public int $y) implements Vec=
tor2 use Evolvable;<br></div><div><br></div><div>When combined with inne=
r classes, it looks something like this:</div><div><br></div><div>class =
Pixel {<br></div><div>&nbsp; public readonly class Point(public int $x, =
public int $y) implements Vector2 use Evolvable;<br></div><div>}<br></di=
v><div><br></div><div>// Create a new pixel point with property $x and $=
y set to 0</div><div>$p =3D new Pixel::Point(0, 0);<br></div><div><br></=
div><div>There are far more details in the RFC itself, so please check i=
t out. I'm quite excited to hear your thoughts!</div><div><br></div><div=
 id=3D"sig121229152">=E2=80=94 Rob<br></div><div id=3D"sig121229152"><br=
></div><div><div>PS. I know I tend to rush into things, but I want to ma=
ke it clear that I'm not rushing this -- I've learned from my mistakes (=
thank you to those who have given me advice). I'm going to do this right=
.<br></div><div><br></div></div><div><br></div></body></html>
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