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Date: Tue, 21 Feb 2023 09:25:21 -0300
Message-ID: <CADK1yX+LmLen4x2tMMj859wG5LC7S-ROauSbCXAvG4Ltm6Mhmg@mail.gmail.com>
To: someniatko <someniatko@gmail.com>
Cc: php internals <internals@lists.php.net>
Content-Type: multipart/alternative; boundary="000000000000508a5005f534e06c"
Subject: Re: [PHP-DEV] Class Re-implementation Mechanism
From: deleugyn@gmail.com (Deleu)

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On Tue, Feb 21, 2023, 8:52 AM someniatko <someniatko@gmail.com> wrote:

> Hi again, internals
>
> My marathon of some crazy ideas continues :D, with less crazy one this
> time.
>
>
> ## Idea
>
> Allow "reimplementing" the non-static public API (that is public
> properties and methods, excluding constructor) of a class by other
> classes like this:
>
> ```php
> final class interface A {
>     public string $s;
>
>     public function __construct(string $s) { $this->s = $s; }
>
>     public static function fromInt(int $i): self { return new
> self((string) $i); }
>
>     public function foo(): int { return 42; }
> }
>
> final class B implements A {
>     public string $s = 'hello';
>
>     public function foo(): int { return 69; }
> }
>
> function usesA(A $param): void {}
>
> usesA(new B); // this works
> ```
>
>
> ## Explanation
>
> Consider there is a class like this:
>
> ```php
> final class Service {
>     public function __construct(private SomeDependency $dependency) {}
>     // ...
> }
>
> final class SomeDependency {
>     // ...
> }
> ```
>
> We want to write some tests for the Service class, but we don't want
> to use a real SomeDependency instance
> during tests. A common approach is to either extract an interface
> (JUST to make it testable), or to drop the
> `final` keyword and allow extending the class.
>
> Both approaches have their flaws:
>  - extracting an interface unnecessarily complicates the system, where
> only one "real" implementation of an interface is assumed.
>  - dropping the `final` keyword allows for the rabbit-hole of
> inheritance abuse, like greatly described in this article:
> https://front-line-php.com/object-oriented
>
> I believe I came up with a better idea: what if we could leave both
> benefits of prohibiting the inheritance abuse and also allow not to
> clutter our namespace with excess entities like interfaces? I hereby
> suggest to combine the responsibilities of a class and an interface
> into one thing like that:
>
> ```php
> final class interface C {}
> final class D implements C {}
> ```
>
> Now other classes can "implement" this class as well. Introduction of
> the new syntax (`class interface`) also solves BC problem - if you
> want to forbid your classes to be reimplemented whatsoever, you can
> still stick to the `final class` syntax. Although it is also possible
> to allow "reimplementing" ANY class, then new syntax is not needed -
> but some library writers like Marco Pivetta could be sad about that I
> suppose.
>
> Soo..., what do you think? Could this be a valuable addition to the
> language?
>
> Regards,
> Illia / someniatko
>
> --
> PHP Internals - PHP Runtime Development Mailing List
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Although I undeterstand and agree with the annoyance of both limitations
presented, I think one important factor that makes this an issue lies with
PSR-4 and autoloading. If you could declare the interface and the
implementation in the same file, as you do with Typescript, the drawback of
extracting an interface for testing would be greatly diminished.
Unfortunately undoing PSR-4 shortcomings and getting something baked into
Composer or PHP to address this seems fairly challenging.

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