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Date: Thu, 22 May 2025 17:25:57 +0200
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Subject: Re: [PHP-DEV] [RFC] Readonly constructors
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From: rob@bottled.codes ("Rob Landers")

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On Thu, May 22, 2025, at 17:01, Mihail Liahimov wrote:
> In PHP 8.1 the class read-on syntax was added, which allows you to cre=
ate classes that are completely closed to changes. In addition, it allow=
s you to write less boilerplate when declaring a property in the constru=
ctor.
>=20
> Before 8.1:
>=20
> class A
> {
>     public function __construct(
>         private readonly int $a,
>         private readonly int $b,
>         private readonly int $c,
>     ) { }
> }
>=20
> After 8.1:
>=20
> readonly class A
> {
>     public function __construct(
>         private int $a,
>         private int $b,
>         private int $c,
>     ) { }
> }
>=20
> But there are also scenarios where, for some reason, not all propertie=
s need to be readonly. For example, when we inherit from a non-readonly =
class or when our class has a state for some kind of memoization. In thi=
s case, the class is not readonly, and as a result, you have to write an=
 extra boiler plate in the constructor. I would like to be able to decla=
re many readon properties in the constructor in a way similar to readon =
classes.
>=20
> I suggest adding the ability to declare a constructor as a readonly. I=
n this case, all the properties declared in it will be automatically rea=
donly.
>=20
> class A extends NonReadonlyClass
> {
>     public readonly function __construct(
>         private int $a,
>         private int $b,
>         private int $c,
>     ) { }
> }
>=20
> Yes, it looks a bit strange, but maybe someone will have other suggest=
ions. Perhaps there is a more competent way to organize this idea.

Hello Mihail,

I feel like it is kinda that way on purpose? If you find yourself writin=
g a constructor with a lot of parameters that are a mix or readonly prop=
erties, it feels like that is a code smell. Either you should consider d=
ecomposing the object into multiple single-purpose objects or rethink th=
e architecture in some way. For example:

> when our class has a state for some kind of memoization.

For example, in this case, you'd wrap the memoization state inside a mut=
able object and then use that as a readonly property.

=E2=80=94 Rob
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<!DOCTYPE html><html><head><title></title></head><body><div>On Thu, May =
22, 2025, at 17:01, Mihail Liahimov wrote:</div><blockquote type=3D"cite=
" id=3D"qt" style=3D""><div dir=3D"ltr"><div>In PHP 8.1 the class read-o=
n syntax was added, which allows you to create classes that are complete=
ly closed to changes. In addition, it allows you to write less boilerpla=
te when declaring a property in the constructor.</div><div><br></div><di=
v>Before 8.1:</div><div><br></div><div>class A</div><div>{</div><div>&nb=
sp; &nbsp; public function __construct(</div><div>&nbsp; &nbsp; &nbsp; &=
nbsp; private readonly int $a,</div><div>&nbsp; &nbsp; &nbsp; &nbsp; pri=
vate readonly int $b,</div><div>&nbsp; &nbsp; &nbsp; &nbsp; private read=
only int $c,</div><div>&nbsp; &nbsp; ) { }</div><div>}</div><div><br></d=
iv><div>After 8.1:</div><div><br></div><div>readonly class A</div><div>{=
</div><div>&nbsp; &nbsp; public function __construct(</div><div>&nbsp; &=
nbsp; &nbsp; &nbsp; private int $a,</div><div>&nbsp; &nbsp; &nbsp; &nbsp=
; private int $b,</div><div>&nbsp; &nbsp; &nbsp; &nbsp; private int $c,<=
/div><div>&nbsp; &nbsp; ) { }</div><div>}</div><div><br></div><div>But t=
here are also scenarios where, for some reason, not all properties need =
to be readonly. For example, when we inherit from a non-readonly class o=
r when our class has a state for some kind of memoization. In this case,=
 the class is not readonly, and as a result, you have to write an extra =
boiler plate in the constructor. I would like to be able to declare many=
 readon properties in the constructor in a way similar to readon classes=
.</div><div><br></div><div>I suggest adding the ability to declare a con=
structor as a readonly. In this case, all the properties declared in it =
will be automatically readonly.</div><div><br></div><div>class A extends=
 NonReadonlyClass</div><div>{</div><div>&nbsp; &nbsp; public readonly fu=
nction __construct(</div><div>&nbsp; &nbsp; &nbsp; &nbsp; private int $a=
,</div><div>&nbsp; &nbsp; &nbsp; &nbsp; private int $b,</div><div>&nbsp;=
 &nbsp; &nbsp; &nbsp; private int $c,</div><div>&nbsp; &nbsp; ) { }</div=
><div>}</div><div><br></div><div>Yes, it looks a bit strange, but maybe =
someone will have other suggestions. Perhaps there is a more competent w=
ay to organize this idea.</div></div></blockquote><div><br></div><div>He=
llo&nbsp;Mihail,</div><div><br></div><div>I feel like it is kinda that w=
ay on purpose? If you find yourself writing a constructor with a lot of =
parameters that are a mix or readonly properties, it feels like that is =
a code smell. Either you should consider decomposing the object into mul=
tiple single-purpose objects or rethink the architecture in some way. Fo=
r example:</div><div><br></div><blockquote type=3D"cite"><div>when our c=
lass has a state for some kind of memoization.</div></blockquote><div><b=
r></div><div>For example, in this case, you'd wrap the memoization state=
 inside a mutable object and then use that as a readonly property.</div>=
<div><br></div><div id=3D"sig121229152">=E2=80=94 Rob</div></body></html=
>
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