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Date: Fri, 21 Apr 2023 12:45:38 +0200
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Subject: Re: [PHP-DEV] [Discussion] Callable types via Interfaces
From: tovilo.ilija@gmail.com (Ilija Tovilo)

Hi Larry and Nicolas!

> https://wiki.php.net/rfc/allow_casting_closures_into_single-method_interface_implementations
> https://wiki.php.net/rfc/allow-closures-to-declare-interfaces-they-implement
> https://wiki.php.net/rfc/structural-typing-for-closures
>
> What we propose is to instead lean into the interface approach.  Specifically, recall that all closures in PHP are actually implemented as classes in the engine.  That is:
>
> $f = fn(int $x, int $y): int => $x + $y;
>
> actually turns into (approximately) this in the engine:
>
> $f = new class extends \Closure
> {
>     public function __invoke(int $x, int $y): int
>     {
>         return $x + $y;
>     }
> }

Just to comment on the technical aspect, I don't think this is
accurate. Closures are indeed objects, but they are all instances of
the same \Closure class. From what Nikita said in the enum RFC,
objects are optimized for size, classes are not. Having different
closures implement different interfaces does mean they probably all
need their own class, or type checks need to account for closures in
some alternative way.

Ilija