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Date: Sun, 03 Aug 2025 13:40:40 +0200
To: "Jonathan Vollebregt" <jnv@jnvsor.net>
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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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I originally wrote a long af reply ... but now I agree that this is a bu=
g as well after writing it out ...

I=E2=80=99ll be referring to the following code:

class A {
  protected int $v =3D 1;
}

class B extends A {}

class C extends A {
  protected int $v =3D 2;
}

class D extends A {
  protected int $v =3D 3 { get =3D> $this->v * 2 }
}

---

Reason 1:
Changing the value changes the contract of it's parent.

This is also possible indirectly without changing the contract in C:

class C extends A {
  public function __construct() {
    $this->v =3D 2;
  }
}

This is effectively the same thing as redeclaring it and setting a diffe=
rent value for $v.

---

Reason 2:
Changing the behaviour changes the contract of it's parent.

This is also possible indirectly without changing the contract in D:

class D extends A {
  private int $_v;
  public function __construct() {
    $this->_v =3D $this->v;
    unset($this->v);
  }
  public function __set($name, $value) {
    $name =3D "_{$name}";
    $this->{$name} =3D $value;
  }
  public function __get($name) {
    $name =3D "_{$name}";
    return $this->{$name};
  }
}

Thus I think since this is already possible, making it more explicit vs.=
 this wordy and round-about way of doing the same thing shouldn=E2=80=99=
t be necessary.

---

In both the examples above, a sibling class would still be able to acces=
s $v, even though the default value and/or behaviour change completely. =
However, if you make it more obvious that this is the case (by using hoo=
ks and/or changing the default value), you can=E2=80=99t access it from =
a sibling.
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<!DOCTYPE html><html><head><title></title></head><body><div>I originally=
 wrote a long af reply ... but now I agree that this is a bug as well af=
ter writing it out ...</div><div><br></div><div>I=E2=80=99ll be referrin=
g to the following code:</div><div><br></div><div>class A {</div><div>&n=
bsp; protected int $v =3D 1;</div><div>}</div><div><br></div><div>class =
B extends A {}</div><div><br></div><div>class C extends A {</div><div>&n=
bsp; protected int $v =3D 2;</div><div>}</div><div><br></div><div>class =
D extends A {</div><div>&nbsp; protected int $v =3D 3 { get =3D&gt; $thi=
s-&gt;v * 2 }</div><div>}</div><div><br></div><div>---</div><div><br></d=
iv><div>Reason 1:</div><div>Changing the value changes the contract of i=
t's parent.</div><div><br></div><div>This is also possible indirectly wi=
thout changing the contract in C:</div><div><br></div><div>class C exten=
ds A {</div><div>&nbsp; public function __construct() {</div><div>&nbsp;=
 &nbsp; $this-&gt;v =3D 2;</div><div>&nbsp; }</div><div>}</div><div><br>=
</div><div>This is effectively the same thing as redeclaring it and sett=
ing a different value for $v.</div><div><br></div><div>---</div><div><br=
></div><div>Reason 2:</div><div>Changing the behaviour changes the contr=
act of it's parent.</div><div><br></div><div>This is also possible indir=
ectly without changing the contract in D:</div><div><br></div><div>class=
 D extends A {</div><div>&nbsp; private int $_v;</div><div>&nbsp; public=
 function __construct() {</div><div>&nbsp; &nbsp; $this-&gt;_v =3D $this=
-&gt;v;</div><div>&nbsp; &nbsp; unset($this-&gt;v);</div><div>&nbsp; }</=
div><div>&nbsp; public function __set($name, $value) {</div><div>&nbsp; =
&nbsp; $name =3D "_{$name}";</div><div>&nbsp; &nbsp; $this-&gt;{$name} =3D=
 $value;</div><div>&nbsp; }</div><div>&nbsp; public function __get($name=
) {</div><div>&nbsp; &nbsp; $name =3D "_{$name}";</div><div>&nbsp; &nbsp=
; return $this-&gt;{$name};</div><div>&nbsp; }</div><div>}</div><div><br=
></div><div>Thus I think since this is already possible, making it more =
explicit vs. this wordy and round-about way of doing the same thing shou=
ldn=E2=80=99t be necessary.</div><div><br></div><div>---</div><div><br><=
/div><div>In both the examples above, a sibling class would still be abl=
e to access $v, even though the default value and/or behaviour change co=
mpletely. However, if you make it more obvious that this is the case (by=
 using hooks and/or changing the default value), you can=E2=80=99t acces=
s it from a sibling.</div></body></html>
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