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Date: Wed, 12 Mar 2025 11:10:48 +0100
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Subject: [PHP-DEV] Re: RFC: short and inner classes
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From: rob@bottled.codes ("Rob Landers")

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On Thu, Mar 6, 2025, at 00:11, Rob Landers wrote:
> Hello PHP Internals,
>=20
> I'd like to introduce my RFC for discussion: https://wiki.php.net/rfc/=
short-and-inner-classes
>=20
> This RFC defines a short class syntax as well as the ability to nest c=
lasses inside another class. This introduces an unprecedented amount of =
control, flexibility, and expressiveness over how objects are used and i=
nstantiated in PHP. There is a PR (https://github.com/php/php-src/pull/1=
7895) that implements this functionality -- all test failures are relate=
d to different/new/incorrect error messages being generated. However, th=
e core functionality exists to take for a test ride.
>=20
> So, what do I mean by "unprecedented amount of control"? With this cha=
nge, you can declare an inner class as private or protected, preventing =
its usage outside of the outer class:
>=20
> class User {
>   private class Id {}
>=20
>   public function __construct(public self::Id $id) {}
> }
>=20
> In the above example, the class `User` 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 hin=
t, or even via `instanceof` outside of the User class itself. This examp=
le isn't practical but demonstrates something that is nearly impossible =
in previous versions of PHP, where all classes are essentially publicly =
accessible from anywhere within the codebase.
>=20
> As a number of inner classes will probably be used as DTOs, the RFC in=
troduces a "short syntax" for declaring classes, which enhances expressi=
veness, even allowing the usage of traits, all in a single line:
>=20
> // declare a readonly Point, that implements Vector2 and uses the Evol=
vable trait
> readonly class Point(public int $x, public int $y) implements Vector2 =
use Evolvable;
>=20
> When combined with inner classes, it looks something like this:
>=20
> class Pixel {
>   public readonly class Point(public int $x, public int $y) implements=
 Vector2 use Evolvable;
> }
>=20
> // Create a new pixel point with property $x and $y set to 0
> $p =3D new Pixel::Point(0, 0);
>=20
> There are far more details in the RFC itself, so please check it out. =
I'm quite excited to hear your thoughts!
>=20
> =E2=80=94 Rob
>=20
> PS. I know I tend to rush into things, but I want to make it clear tha=
t I'm not rushing this -- I've learned from my mistakes (thank you to th=
ose who have given me advice). I'm going to do this right.
>=20
>=20

Hello internals,

I've made some major updates to the text of the RFC to clarify behaviors=
 and revisited the implementation (which is still under development, tho=
ugh I hope to have a draft by the end of this weekend). Here's a broad o=
verview of what has changed in inner classes:

- Accessing inner classes is done via a new token: ":>" instead of "::".
- Inner classes may now be infinitely nested.
- Inner classes may be declared `abstract`.
- Documented changes to ReflectionClass.
- Usage of `static` to refer to inner classes is restricted to prevent a=
ccidental violations of LSP.

Otherwise, there are not any big changes, but a lot of time was spent cl=
arifying behavior and expanding on the reasoning for those decisions in =
the RFC itself.

=E2=80=94 Rob
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<!DOCTYPE html><html><head><title></title><style type=3D"text/css">=0Ap.=
MsoNormal,p.MsoNoSpacing{margin:0}</style></head><body><div>On Thu, Mar =
6, 2025, at 00:11, Rob Landers wrote:<br></div><blockquote type=3D"cite"=
 id=3D"qt" style=3D""><div>Hello PHP Internals,<br></div><div><br></div>=
<div>I'd like to introduce my RFC for discussion:&nbsp;<a href=3D"https:=
//wiki.php.net/rfc/short-and-inner-classes">https://wiki.php.net/rfc/sho=
rt-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 anothe=
r 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.com/php/php-src/pull/17895">htt=
ps://github.com/php/php-src/pull/17895</a>) that implements this functio=
nality -- all test failures are related to different/new/incorrect error=
 messages being generated. However, the core functionality exists to tak=
e for a test ride.<br></div><div><br></div><div>So, what do I mean by "u=
nprecedented amount of control"? With this change, you can declare an in=
ner class as private or protected, preventing its usage outside of the o=
uter class:<br></div><div><br></div><div>class User {<br></div><div>&nbs=
p; private class Id {}<br></div><div><br></div><div>&nbsp; public functi=
on __construct(public self::Id $id) {}<br></div><div>}<br></div><div><br=
></div><div>In the above example, the class `User` is impossible to cons=
truct 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 i=
mpossible in previous versions of PHP, where all classes are essentially=
 publicly accessible from anywhere within the codebase.<br></div><div><b=
r></div><div>As a number of inner classes will probably be used as DTOs,=
 the RFC introduces a "short syntax" for declaring classes, which enhanc=
es expressiveness, even allowing the usage of traits, all in a single li=
ne:<br></div><div><br></div><div>// declare a readonly Point, that imple=
ments Vector2 and uses the Evolvable trait<br></div><div>readonly class =
Point(public int $x, public int $y) implements Vector2 use Evolvable;<br=
></div><div><br></div><div>When combined with inner classes, it looks so=
mething like this:<br></div><div><br></div><div>class Pixel {<br></div><=
div>&nbsp; public readonly class Point(public int $x, public int $y) imp=
lements Vector2 use Evolvable;<br></div><div>}<br></div><div><br></div><=
div>// Create a new pixel point with property $x and $y set to 0<br></di=
v><div>$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 it out. I'm qui=
te excited to hear your thoughts!<br></div><div><br></div><div id=3D"qt-=
sig121229152">=E2=80=94 Rob<br></div><div id=3D"qt-sig121229152"><br></d=
iv><div><div>PS. I know I tend to rush into things, but I want to make i=
t clear that I'm not rushing this -- I've learned from my mistakes (than=
k you to those who have given me advice). I'm going to do this right.<br=
></div><div><br></div></div><div><br></div></blockquote><div><br></div><=
div>Hello internals,<br></div><div><br></div><div>I've made some major u=
pdates to the text of the RFC to clarify behaviors and revisited the imp=
lementation (which is still under development, though I hope to have a d=
raft by the end of this weekend). Here's a broad overview of what has ch=
anged in inner classes:<br></div><div><br></div><div>- Accessing inner c=
lasses is done via a new token: ":&gt;" instead of "::".<br></div><div>-=
 Inner classes may now be infinitely nested.<br></div><div>- Inner class=
es may be declared `abstract`.<br></div><div>- Documented changes to Ref=
lectionClass.<br></div><div>- Usage of `static` to refer to inner classe=
s is restricted to prevent accidental violations of LSP.</div><div><br><=
/div><div>Otherwise, there are not any big changes, but a lot of time wa=
s spent clarifying behavior and expanding on the reasoning for those dec=
isions in the RFC itself.</div><div><br></div><div id=3D"sig121229152">=E2=
=80=94 Rob<br></div></body></html>
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