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Sun, 9 Nov 2025 15:31:48 -0500 (EST) X-Mailer: MessagingEngine.com Webmail Interface Precedence: list list-help: list-unsubscribe: list-post: List-Id: x-ms-reactions: disallow MIME-Version: 1.0 X-ThreadId: AZgO4gJIj6HZ Date: Sun, 09 Nov 2025 21:31:27 +0100 To: =?UTF-8?Q?Tim_D=C3=BCsterhus?= , =?UTF-8?Q?Alexandru_P=C4=83tr=C4=83nescu?= Cc: "PHP internals" Message-ID: <378db9d8-21e3-4faf-a6b0-eaec6e4560af@app.fastmail.com> In-Reply-To: <475570ea-ff3f-4eb2-bbe6-8f86760ac5e3@bastelstu.be> References: <7e17ab87-294f-450d-9afc-d23a5b919cc5@app.fastmail.com> <475570ea-ff3f-4eb2-bbe6-8f86760ac5e3@bastelstu.be> Subject: Re: [PHP-DEV] RFC: Namespace-Scoped Visibility for Methods and Properties Content-Type: multipart/alternative; boundary=018cb6da37c34a19a6e12537bbd40e8b From: rob@bottled.codes ("Rob Landers") --018cb6da37c34a19a6e12537bbd40e8b Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable On Sun, Nov 9, 2025, at 20:55, Tim D=C3=BCsterhus wrote: > Hi >=20 > On 11/9/25 20:41, Rob Landers wrote: > > class P { > > private(namespace) function x() {} > > } > >=20 > > class C extends P { > > protected function x() {} > > } > >=20 > > This behaves the same as overriding a private method with a protecte= d/public one today: the parent=E2=80=99s method is private to its declar= ing class, so the second example is allowed. >=20 > This is unsound. As we have established, neither `private(namespace)`=20 > nor `protected` is a subset of each other. >=20 > Specifically allowing this breaks the following (everything is declare= d=20 > in the same namespace): >=20 > class P { > private(namespace) function x() { } > } > class C extends P { > protected function x() { } > } >=20 > function f(P $p) { > $p->x(); // legal, because f is in the same namespace as P. > } >=20 > f(new C()); // breaks, because C::x() is protected and thus not=20 > legal to access from f / the global scope. >=20 > Best regards > Tim D=C3=BCsterhus Initially, I treated `private(namespace)` like `private` for cross-names= pace inheritance and overlooked how dynamic dispatch actually works in P= HP. This means that a same-named method in a child would simply be a new= method. But like you point out, that leads to a subtle problem. Even though `P::x()` is a method that=E2=80=99s visible and intended for= callers inside namespace A, the runtime dispatch would pick `C::x()`. T= hat completely and utterly destroys substitutability for namespace inter= nal callers, which is exactly what this visibility is meant to protect. So ... it seems we need a couple of additional rules here: 1. If a parent has a `private(namespace)` method, then a subclass in a d= ifferent namespace simply cannot declare a method with the exact same na= me. It=E2=80=99d be a compile time error to prevent shadowing and keep d= ispatch predictable. I=E2=80=99d also be open to other ways as well (suc= h as always calling the namespaced method in the parent), but I=E2=80=99= d need to see if that=E2=80=99s even possible in the engine. 2. As you pointed out, `protected `and` private(namespace)` aren=E2=80=99= t compatible; thus we should only allow the same or a superset. So, it s= hould only allow `public` or `private(namespace)` when inheriting in the= same namespace. =E2=80=94 Rob --018cb6da37c34a19a6e12537bbd40e8b Content-Type: text/html; charset=utf-8 Content-Transfer-Encoding: quoted-printable
On Sun, Nov = 9, 2025, at 20:55, Tim D=C3=BCsterhus wrote:
Hi

On 11/9/25 20:= 41, Rob Landers wrote:
> class P {
> &nbs= p;    private(namespace) function x() {}
> }=
> 
> class C extends P {
>&= nbsp;     protected function x() {}
> }=
> 
> This behaves the same as overriding= a private method with a protected/public one today: the parent=E2=80=99= s method is private to its declaring class, so the second example is all= owed.

This is unsound. As we have established, = neither `private(namespace)` 
nor `protected` is a subset= of each other.

Specifically allowing this brea= ks the following (everything is declared 
in the same nam= espace):

     class P {
         private(namespac= e) function x() { }
     }
 = ;    class C extends P {
   &nbs= p;     protected function x() { }
 &n= bsp;   }

     fun= ction f(P $p) {
       &nbs= p; $p->x(); // legal, because f is in the same namespace as P.
<= div>     }

  &nbs= p;  f(new C()); // breaks, because C::x() is protected and thus not=  
legal to access from f / the global scope.
Best regards
Tim D=C3=BCsterhus

Initially, I treated private(namespace) like private for cross-namespace inhe= ritance and overlooked how dynamic dispatch actually works in PHP. This = means that a same-named method in a child would simply be a new method. = But like you point out, that leads to a subtle problem.

Even though P::x() is a method that=E2=80=99s visible and intended for calle= rs inside namespace A, the runtime dispatch would pick C::x(). That completely and ut= terly destroys substitutability for namespace internal callers, which is= exactly what this visibility is meant to protect.

<= div>So ... it seems we need a couple of additional rules here:

1. If a parent has a private(namespace) method, then a subclass in a = different namespace simply cannot declare a method with the exact same n= ame. It=E2=80=99d be a compile time error to prevent shadowing and keep = dispatch predictable. I=E2=80=99d also be open to other ways as well (su= ch as always calling the namespaced method in the parent), but I=E2=80=99= d need to see if that=E2=80=99s even possible in the engine.
<= br>
2. As you pointed out, protected and private(namespace) aren=E2=80=99t compatible; t= hus we should only allow the same or a superset. So, it should only allo= w public or <= code style=3D"border-top-width:1px;border-right-width:1px;border-bottom-= width:1px;border-left-width:1px;border-top-style:solid;border-right-styl= e:solid;border-bottom-style:solid;border-left-style:solid;border-top-col= or:#ccc;border-right-color:#ccc;border-bottom-color:#ccc;border-left-col= or:#ccc;border-image-source:initial;border-image-slice:initial;border-im= age-width:initial;border-image-outset:initial;border-image-repeat:initia= l;border-top-left-radius:3px;border-top-right-radius:3px;border-bottom-r= ight-radius:3px;border-bottom-left-radius:3px;background-image:initial;b= ackground-position-x:initial;background-position-y:initial;background-si= ze:initial;background-repeat:initial;background-attachment:initial;backg= round-origin:initial;background-clip:initial;background-color:#f6f6f6;fo= nt-family:menlo, consolas, monospace;font-size:90%;padding-top:1px;paddi= ng-right:3px;padding-bottom:1px;padding-left:3px;">private(namespace) when inheriting in the same namespace.

=E2=80=94 Rob --018cb6da37c34a19a6e12537bbd40e8b--