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Date: Tue, 3 Feb 2026 10:22:24 +0100
Message-ID: <CAOWwgpn-agceHfEvRhyU0UEJCCif=6znH15=-m2B8ScEngUcEw@mail.gmail.com>
Subject: Re: [PHP-DEV] [RFC] Allow Reassignment of Promoted Readonly
 Properties in Constructor
To: Rob Landers <rob@bottled.codes>
Cc: PHP Internals List <internals@lists.php.net>
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From: nicolas.grekas+php@gmail.com (Nicolas Grekas)

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Le mar. 3 f=C3=A9vr. 2026 =C3=A0 10:00, Rob Landers <rob@bottled.codes> a =
=C3=A9crit :

> On Tue, Feb 3, 2026, at 09:56, Nicolas Grekas wrote:
>
> Hi Rob,
>
> Le mar. 3 f=C3=A9vr. 2026 =C3=A0 09:50, Rob Landers <rob@bottled.codes> a=
 =C3=A9crit :
>
>
> On Mon, Feb 2, 2026, at 22:14, Nicolas Grekas wrote:
>
> Hi Marco,
>
> Le lun. 2 f=C3=A9vr. 2026 =C3=A0 11:54, Marco Pivetta <ocramius@gmail.com=
> a =C3=A9crit :
>
> Hey Nicolas,
>
>
> On Thu, 22 Jan 2026 at 16:34, Nicolas Grekas <nicolas.grekas+php@gmail.co=
m>
> wrote:
>
> Dear all,
>
> Here is a new RFC for you to consider:
> https://wiki.php.net/rfc/promoted_readonly_constructor_reassign
>
>
>
> What happens if one calls `$obj->__construct(1, 2, 3)` (on an already
> instantiated `$obj`) in the context of this patch?
>
>
> Thanks for asking, I didn't think about this. This made me also think
> about ReflectionClass::newInstanceWithoutConstructor().
> I clarified this in the RFC, see "Direct __construct() Calls Cannot Bypas=
s
> Readonly" and "Reflection: Objects Created Without Constructor".
> Patch and PR updated also if anyone wants to run some code where this RFC
> can be played with.
>
> Cheers,
> Nicolas
>
>
> Hi Nicolas,
>
> Under "Child Classes Can Reassign Parent Properties": this feels like a
> major footgun. Calling parent::__construct() won't allow a reset (per the
> rules of calling a constructor directly); which would completely break
> inheritance... but then in the examples it says that calling a constructo=
r
> directly can reset it -- but you can't?
>
> This feels really inconsistent to me.
>
> =E2=80=94 Rob
>
>
> Yes, the text was ambiguous. The implementation allows
> parent::__construct() during the initial construction (normal inheritance=
),
> and only blocks explicit __construct() calls after construction completed=
.
> I=E2=80=99ve clarified this in the RFC.
>
> Nicolas
>
>
> Will this result in a catchable error? I assume so, so a valid pattern
> during inheritance might be to put these in a try/catch so children can s=
et
> them first?
>
> FWIW, in my Records RFC, properties were fully mutable during constructio=
n
> for exactly this reason.
>
>
The existing behavior is preserved: if a reassignment fails, it throws a
catchable Error. The implicit CPP assignment in a parent constructor
happens before the parent body, so a child cannot "set first" and then call
''parent::__construct()'' to avoid it; a try/catch in the parent cannot
intercept it. But a try/catch in the child can catch of course.

Does that answer your question?

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<div dir=3D"ltr"><div dir=3D"ltr"><br></div><br><div class=3D"gmail_quote g=
mail_quote_container"><div dir=3D"ltr" class=3D"gmail_attr">Le=C2=A0mar. 3 =
f=C3=A9vr. 2026 =C3=A0=C2=A010:00, Rob Landers &lt;rob@bottled.codes&gt; a =
=C3=A9crit=C2=A0:<br></div><blockquote class=3D"gmail_quote" style=3D"margi=
n:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex=
"><u></u><div><div>On Tue, Feb 3, 2026, at 09:56, Nicolas Grekas wrote:</di=
v><blockquote type=3D"cite" id=3D"m_2981261145739922581qt"><div dir=3D"ltr"=
><div dir=3D"ltr">Hi Rob,</div><div><br></div><div><div dir=3D"ltr">Le=C2=
=A0mar. 3 f=C3=A9vr. 2026 =C3=A0=C2=A009:50, Rob Landers &lt;rob@bottled.co=
des&gt; a =C3=A9crit=C2=A0:</div><blockquote style=3D"margin:0px 0px 0px 0.=
8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div><u></u><b=
r></div><div><div>On Mon, Feb 2, 2026, at 22:14, Nicolas Grekas wrote:</div=
><blockquote type=3D"cite" id=3D"m_2981261145739922581qt-m_6564486400604031=
585qt"><div dir=3D"ltr"><div dir=3D"ltr">Hi Marco,</div><div><br></div><div=
><div dir=3D"ltr">Le=C2=A0lun. 2 f=C3=A9vr. 2026 =C3=A0=C2=A011:54, Marco P=
ivetta &lt;<a href=3D"mailto:ocramius@gmail.com" target=3D"_blank">ocramius=
@gmail.com</a>&gt; a =C3=A9crit=C2=A0:</div><blockquote style=3D"margin:0px=
 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><di=
v dir=3D"ltr"><div dir=3D"ltr"><div>Hey Nicolas,</div><div><br></div></div>=
<div><br></div><div><div dir=3D"ltr">On Thu, 22 Jan 2026 at 16:34, Nicolas =
Grekas &lt;<a href=3D"mailto:nicolas.grekas%2Bphp@gmail.com" target=3D"_bla=
nk">nicolas.grekas+php@gmail.com</a>&gt; wrote:</div><blockquote style=3D"m=
argin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left=
:1ex"><div dir=3D"ltr"><div>Dear all,</div><div><br></div><div>Here is a=C2=
=A0new RFC for you to consider:</div><div><a href=3D"https://wiki.php.net/r=
fc/promoted_readonly_constructor_reassign" target=3D"_blank">https://wiki.p=
hp.net/rfc/promoted_readonly_constructor_reassign</a></div></div></blockquo=
te><div><br></div><div><div><br></div><div>What happens if one calls `$obj-=
&gt;__construct(1, 2, 3)` (on an already instantiated `$obj`) in the contex=
t of this patch?</div></div></div></div></blockquote><div><br></div><div>Th=
anks for asking, I didn&#39;t think about this. This made me also think abo=
ut ReflectionClass::newInstanceWithoutConstructor().</div><div>I clarified =
this in the RFC, see &quot;Direct __construct() Calls Cannot Bypass Readonl=
y&quot; and &quot;Reflection: Objects Created Without Constructor&quot;.</d=
iv><div>Patch and PR updated also if anyone wants to run some code where th=
is RFC can be played with.</div><div><br></div><div>Cheers,</div><div>Nicol=
as</div></div></div></blockquote><div><br></div><div>Hi Nicolas,</div><div>=
<br></div><div>Under &quot;Child Classes Can Reassign Parent Properties&quo=
t;: this feels like a major footgun. Calling parent::__construct() won&#39;=
t allow a reset (per the rules of calling a constructor directly); which wo=
uld completely break inheritance... but then in the examples it says that c=
alling a constructor directly can reset it -- but you can&#39;t?</div><div>=
<br></div><div>This feels really inconsistent to me.</div><div><br></div><d=
iv id=3D"m_2981261145739922581qt-m_6564486400604031585sig121229152">=E2=80=
=94 Rob</div></div></blockquote><div><br></div><div>Yes, the text was ambig=
uous. The implementation allows parent::__construct() during the initial co=
nstruction (normal inheritance), and only blocks explicit __construct() cal=
ls after construction completed. I=E2=80=99ve clarified this in the RFC.</d=
iv><div><br></div><div>Nicolas</div></div></div></blockquote><div><br></div=
><div>Will this result in a catchable error? I assume so, so a valid patter=
n during inheritance might be to put these in a try/catch so children can s=
et them first?</div><div><br></div><div>FWIW, in my Records RFC, properties=
 were fully mutable during construction for exactly this reason.=C2=A0</div=
><div><br></div><div id=3D"m_2981261145739922581sig121229152"></div></div><=
/blockquote><div><br></div><div>The existing behavior is preserved: if a re=
assignment fails, it throws a catchable Error. The implicit CPP assignment =
in a parent constructor happens before the parent body, so a child cannot &=
quot;set first&quot; and then call &#39;&#39;parent::__construct()&#39;&#39=
; to avoid it; a try/catch in the parent cannot intercept it. But a try/cat=
ch in the child can catch of course.</div><div><br></div><div>Does that ans=
wer your question?</div></div></div>

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