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Date: Sat, 02 Aug 2025 16:09:43 +0200
To: =?UTF-8?Q?Alexandru_P=C4=83tr=C4=83nescu?= <drealecs@gmail.com>
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Subject: Re: [PHP-DEV] Protected inheritance hierarchies
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From: rob@bottled.codes ("Rob Landers")

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On Sat, Aug 2, 2025, at 16:04, Alexandru P=C4=83tr=C4=83nescu wrote:
>=20
>=20
> On Sat, Aug 2, 2025 at 12:10=E2=80=AFPM Rob Landers <rob@bottled.codes=
> wrote:
>> __
>> On Tue, Jul 29, 2025, at 20:11, Jonathan Vollebregt wrote:
>>> I came across this edge case today:
>>>=20
>>> https://3v4l.org/R3Q8D
>>>=20
>>> Both psalm and phpstan think this code is A-OK (Once you add the=20
>>> requisite type hints) but it causes fatal errors way back to PHP 5.0=
.0
>>>=20
>>> ...<snip>...
>>=20
>> It's not an edge case, in C2, you redefine a protected variable with =
the same name and shadowed the original $v. That $v is different than C'=
s $v. It's easiest to see this with static access: https://3v4l.org/0SRW=
b#v8.4.10
>>=20
>> However, I don't know of any way to unshadow a property from $this to=
 access the ancestor's value (other than using private access), but it e=
xists and takes up memory; just accessing it is the hard part.
>>=20
>> =E2=80=94 Rob
>=20
>=20
> Hi Rob,
>=20
> I'm pretty sure that there is no shadowing happening in the example.
> When the child instance is created, there is just one slot for the pro=
perty, as the child one replaces the parent one.
> So basically the child property overrides the parent property rather t=
han shadowing it.
>=20
> True shadowing (two slots) only occurs when the parent property is dec=
lared private.
>=20
> It's just that when redefining, it stores the declaring class, and so =
there is this sibling class access issue.
>=20
> I'm wondering now if the access shouldn't be relaxed, in case we have =
the parent class that initially defined the property.
>=20
> Of course, we should focus on non-static properties, as static ones ar=
e different things, and there is some shadowing there.
>=20
> --=20
> Alex

Hi Alex,

I=E2=80=99m not sure what you mean? https://3v4l.org/WKILh#v8.4.10

There is clearly shadowing going on.

=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, Aug 2, 2025, at 16:04, Alexandru P=C4=83tr=C4=83=
nescu wrote:</div><blockquote type=3D"cite" id=3D"qt" style=3D""><div di=
r=3D"ltr"><div dir=3D"ltr"><br></div><div><br></div><div class=3D"qt-gma=
il_quote qt-gmail_quote_container"><div dir=3D"ltr" class=3D"qt-gmail_at=
tr">On Sat, Aug 2, 2025 at 12:10=E2=80=AFPM Rob Landers &lt;rob@bottled.=
codes&gt; wrote:</div><blockquote class=3D"qt-gmail_quote" style=3D"marg=
in-top:0px;margin-right:0px;margin-bottom:0px;margin-left:0.8ex;border-l=
eft-width:1px;border-left-style:solid;border-left-color:rgb(204, 204, 20=
4);padding-left:1ex;"><div><u></u><br></div><div><div>On Tue, Jul 29, 20=
25, at 20:11, Jonathan Vollebregt wrote:</div><blockquote type=3D"cite" =
id=3D"qt-m_6994282754719696319qt"><div>I came across this edge case toda=
y:</div><div><br></div><div><a href=3D"https://3v4l.org/R3Q8D" target=3D=
"_blank">https://3v4l.org/R3Q8D</a></div><div><br></div><div>Both psalm =
and phpstan think this code is A-OK (Once you add the&nbsp;</div><div>re=
quisite type hints) but it causes fatal errors way back to PHP 5.0.0</di=
v><div><br></div><div>...&lt;snip&gt;...</div></blockquote><div><br></di=
v><div>It's not an edge case, in C2, you redefine a protected variable w=
ith the same name and shadowed the original $v. That $v is different tha=
n C's $v. It's easiest to see this with static access:&nbsp;<a href=3D"h=
ttps://3v4l.org/0SRWb#v8.4.10" target=3D"_blank">https://3v4l.org/0SRWb#=
v8.4.10</a></div><div><br></div><div>However, I don't know of any way to=
 unshadow a property from $this to access the ancestor's value (other th=
an using private access), but it exists and takes up memory; just access=
ing it is the hard part.</div><div><br></div><div id=3D"qt-m_69942827547=
19696319sig121229152">=E2=80=94 Rob</div></div></blockquote><div><br></d=
iv><div><br></div><div>Hi Rob,</div><div><br></div><div>I'm pretty sure =
that there is no shadowing happening in the example.</div><div><div>When=
 the child instance is created, there is just one slot for the property,=
 as the child one replaces the parent one.</div><div>So basically the ch=
ild property overrides the parent property=20=0A=0Arather than shadowing=
 it.</div></div><div><br></div><div>True shadowing (two slots) only occu=
rs when the parent property is declared private.</div><div><br></div><di=
v>It's just that when redefining, it stores the declaring class, and so =
there is this sibling class access issue.</div><div><br></div><div>I'm w=
ondering now if the access shouldn't be relaxed, in case we have the par=
ent class that initially defined the property.</div><div><br></div><div>=
Of course, we should focus on non-static properties, as static ones are =
different things, and there is some shadowing there.</div><div><br></div=
><div>--&nbsp;</div><div>Alex</div></div></div></blockquote><div><br></d=
iv><div>Hi Alex,</div><div><br></div><div>I=E2=80=99m not sure what you =
mean?&nbsp;<a href=3D"https://3v4l.org/WKILh#v8.4.10">https://3v4l.org/W=
KILh#v8.4.10</a></div><div><br></div><div>There is clearly shadowing goi=
ng on.<br></div><div><br></div><div id=3D"sig121229152">=E2=80=94 Rob</d=
iv></body></html>
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