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Date: Mon, 24 Mar 2025 19:22:12 +0000
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Subject: Re: [PHP-DEV] Re: RFC: short and inner classes
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From: imsop.php@rwec.co.uk ("Rowan Tommins [IMSoP]")



On 24 March 2025 09:20:03 GMT, "Alexandru P=C4=83tr=C4=83nescu" <drealecs@=
gmail=2Ecom> wrote:
>On Sun, Mar 23, 2025 at 5:20=E2=80=AFPM Larry Garfield <larry@garfieldtec=
h=2Ecom>
>wrote:
>
>>
>> So, how would nested classes compare to fileprivate, in terms of abilit=
y
>> to solve the problem space?  As I understand it, the goal is:
>>
>> 1=2E Classes that can be instantiated only by the class that uses them=
=2E
>> 2=2E But can be returned from that class to a caller and reused as
>> appropriate=2E
>>
>
>
>I think the one other difference is that nested classes can access privat=
e
>variables or their outer classes=2E

You can achieve the same with "file private" access: in your example mark =
the constructor as "file private", and put the Builder in the same file

fileprivate function __construct(private array $points) {}


If you'll excuse a brief philosophical detour, I noticed something interes=
ting in the Swift documentation: the description of nested classes doesn't =
describe any special scope access=2E Instead, the description of "access le=
vels" defines "private" in a way that naturally includes them:

> Private access restricts the use of an entity to the enclosing declarati=
on, and to extensions of that declaration that are in the same file=2E

It's a subtly different framing - nested types aren't breaking into the pr=
ivate entity, the "private" keyword is explicitly letting nested types in=
=2E

A language could, if it chose, have different keywords for "private to exa=
ctly this type" and "private to this type and any nested types":

strict_private function __construct(private array $points) {}
private_or_nested function __construct(private array $points) {}

Just as there are many combinations like "this class, subclasses, or other=
 classes in this module"=2E


The point being that there's nothing fundamental about nested types that g=
ives them access to private properties=2E What they do is give us a new dim=
ension to define access levels of our choice - { contains, contained by, ne=
ither }=2E

File scope gives us instead the dimension { same file, different file }; a=
nd module scope gives us { same module, different module, no module }, and =
maybe some additional relationships between modules=2E


Rowan Tommins
[IMSoP]