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Date: Sat, 19 Jul 2025 12:12:40 +0200
To: "Claude Pache" <claude.pache@gmail.com>
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 "Larry Garfield" <larry@garfieldtech.com>,
 =?UTF-8?Q?Tim_D=C3=BCsterhus?= <tim@bastelstu.be>,
 "php internals" <internals@lists.php.net>
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Subject: Re: [PHP-DEV] [RFC] Readonly property hooks
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From: rob@bottled.codes ("Rob Landers")

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On Sat, Jul 19, 2025, at 12:09, Claude Pache wrote:
>=20
>=20
>> Le 19 juil. 2025 =C3=A0 09:46, Rob Landers <rob@bottled.codes> a =C3=A9=
crit :
>>=20
>>=20
>>=20
>> On Sat, Jul 19, 2025, at 03:04, Claude Pache wrote:
>>>=20
>>>=20
>>>=20
>>>> Le 19 juil. 2025 =C3=A0 00:41, Rob Landers <rob@bottled.codes> a =C3=
=A9crit :
>>>>=20
>>>> The original author (Nikita) suggested that there's nothing in the =
original design that precludes accessors -- and highlights languages whe=
re there are both and they are doing just fine more than 5 years later.
>>>>=20
>>>=20
>>> Hi Rob,
>>>=20
>>> It is indeed entirely reasonable to have both readonly properties an=
d hooked properties (aka accessors), and today PHP has indeed both of th=
em (and even asymmetric visibility on top of that, as a separate feature=
 contrarily to C#). But it doesn=E2=80=99t mean that it is reasonable fo=
r the *same* property to be *both* readonly and hooked, which is the poi=
nt that is currently disputed. =E2=80=94 What do the other languages all=
ow? Is it possible to define a readonly property with a user-defined get=
ter? (Disclaimer: Even if one of them allows such a thing, I=E2=80=99ll =
still think that it is a bad idea.)
>>>=20
>>> =E2=80=94Claude=20
>>=20
>> Hey Claude,
>>=20
>> From what I've seen in other languages, this combination is fairly co=
mmon and not inherently poblematic.
>>=20
>> - C# allows get hooks with user-defined logic, even in readonly struc=
ts.
>> - Kotlin uses val with a get() body, which is readonly from the consu=
mer's perspective, even though the value is computed.
>> - TypeScript allows a get-only accessor which acts readonly.
>> - Swift also allows get-only computed accessors/hooks.
>=20
> Hi Rob,=20
>=20
> The main problem is that we don=E2=80=99t agree on the meaning of =E2=80=
=9Creadonly property=E2=80=9D.
>=20
> I=E2=80=99ve check TypeScript:
>=20
> * It has getters and setters, which correspond to PHP get/set hooks wi=
thout backing store.
>=20
> * Separately, it also has a `readonly` modifier that can be applied to=
 properties; the semantics is that such a property may be initialised ei=
ther at declaration or inside the constructor, but cannot be modified af=
terwards. That corresponds approximatively to PHP readonly properties.
>=20
> * But a =E2=80=9Cget-only accessor=E2=80=9D is not the same thing as a=
 =E2=80=9Creadonly property=E2=80=9D in the specific sense of =E2=80=9Da=
 property decorated with the `readonly` modifier=E2=80=9D. Also, you can=
not add the readonly modifier to a get accessor.
>=20
> =E2=80=94Claude
>=20

The error you get when trying to modify the "get-only accessor" is `Erro=
r: Cannot assign to 'name' because it is a read-only property`

Thus, readonly is implied by the get-only accessor, there's no need to s=
pecify it directly.

=E2=80=94 Rob
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<!DOCTYPE html><html><head><title></title></head><body><div><br></div><d=
iv><br></div><div>On Sat, Jul 19, 2025, at 12:09, Claude Pache wrote:</d=
iv><blockquote type=3D"cite" id=3D"qt" style=3D"overflow-wrap:break-word=
;"><div><br></div><div><div><br></div><blockquote type=3D"cite"><div>Le =
19 juil. 2025 =C3=A0 09:46, Rob Landers &lt;rob@bottled.codes&gt; a =C3=A9=
crit :</div><div><br></div><div><div><div><br></div><div><br></div><div>=
On Sat, Jul 19, 2025, at 03:04, Claude Pache wrote:</div><blockquote typ=
e=3D"cite" id=3D"qt-qt" style=3D""><div dir=3D"ltr"><div dir=3D"ltr"><br=
></div><div dir=3D"ltr"><br></div><div dir=3D"ltr"><div><br></div><block=
quote type=3D"cite"><div>Le 19 juil. 2025 =C3=A0 00:41, Rob Landers &lt;=
rob@bottled.codes&gt; a =C3=A9crit&nbsp;:</div></blockquote></div><block=
quote type=3D"cite"><div dir=3D"ltr"><div class=3D"qt-qt-align-start" st=
yle=3D"text-align:start;"><br></div><div class=3D"qt-qt-align-start" sty=
le=3D"text-align:start;">The original author (Nikita) suggested that the=
re's nothing in the original design that precludes accessors -- and high=
lights languages where there are both and they are doing just fine more =
than 5 years later.</div><div class=3D"qt-qt-align-start" style=3D"text-=
align:start;"><br></div></div></blockquote><div><br></div><div>Hi Rob,</=
div><div><br></div><div>It is indeed entirely reasonable to have both re=
adonly properties and hooked properties (aka accessors), and today PHP h=
as indeed both of them (and even asymmetric visibility on top of that, a=
s a separate feature contrarily to C#). But it doesn=E2=80=99t mean that=
 it is reasonable for the *same* property to be *both* readonly and hook=
ed, which is the point that is currently disputed. =E2=80=94 What do the=
 other languages allow? Is it possible to define a readonly property wit=
h a user-defined getter? (Disclaimer: Even if one of them allows such a =
thing, I=E2=80=99ll still think that it is a bad idea.)</div><div><br></=
div><div>=E2=80=94Claude&nbsp;</div></div></blockquote><div><br></div><d=
iv>Hey Claude,</div><div><br></div><div>From what I've seen in other lan=
guages, this combination is fairly common and not&nbsp;inherently poblem=
atic.</div><div><br></div><div>- C# allows get hooks with user-defined l=
ogic, even in readonly structs.</div><div>- Kotlin uses val with a get()=
 body, which is readonly from the consumer's perspective, even though th=
e value is computed.</div><div>- TypeScript allows a get-only accessor w=
hich acts readonly.</div><div>- Swift also allows get-only computed acce=
ssors/hooks.</div></div></div></blockquote><div><br></div><div>Hi Rob,&n=
bsp;</div><div><br></div><div>The main problem is that we don=E2=80=99t =
agree on the meaning of =E2=80=9Creadonly property=E2=80=9D.</div><div><=
br></div><div>I=E2=80=99ve check TypeScript:</div><div><br></div><div>* =
It has getters and setters, which correspond to PHP get/set hooks withou=
t backing store.</div><div><br></div><div>* Separately, it also has a `r=
eadonly` modifier that can be applied to properties; the semantics is th=
at such a property may be initialised either at declaration or inside th=
e constructor, but cannot be modified afterwards. That corresponds appro=
ximatively to PHP readonly properties.</div><div><br></div><div>* But a =
=E2=80=9Cget-only accessor=E2=80=9D is not the same thing as a =E2=80=9C=
readonly property=E2=80=9D in the specific sense of =E2=80=9Da property =
decorated with the `readonly` modifier=E2=80=9D. Also, you cannot add th=
e readonly modifier to a get accessor.</div><div><br></div><div>=E2=80=94=
Claude</div><div><br></div></div></blockquote><div><br></div><div>The er=
ror you get when trying to modify the "get-only accessor" is `<span clas=
s=3D"color" style=3D"color:rgb(106, 115, 125);"><span class=3D"highlight=
" style=3D"background-color:rgb(245, 245, 245);"></span>Error: Cannot as=
sign to 'name' because it is a read-only property`</span><br></div><div>=
<br></div><div>Thus, readonly is implied by the get-only accessor, there=
's no need to specify it directly.</div><div><br></div><div id=3D"sig121=
229152">=E2=80=94 Rob</div></body></html>
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