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Date: Fri, 21 Mar 2025 12:50:39 +0100
To: Matt Fonda <matthewfonda@gmail.com>
Cc: Daniel Scherzer <daniel.e.scherzer@gmail.com>, internals@lists.php.net
Subject: Re: [PHP-DEV] [RFC] [Discussion] Never parameters
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From: tim@bastelstu.be (=?UTF-8?Q?Tim_D=C3=BCsterhus?=)

Hi

Am 2025-03-20 21:27, schrieb Matt Fonda:
> If an interface adds a method but makes no promises about what 
> parameters
> it accepts, then why is it part of the interface in the first 
> place--why
> add a method that can't be used?

It would more cleanly allow for userland / PHPDoc-based generics, while 
still providing some engine-enforced type safety. Consider this example 
(not sure if I got the syntax completely right):

     /** @template T */
     interface Comparable {
         /** @param T $other */
         public function compareTo(never $other): int;
     }

     /** @implements Comparable<Number> */
     final class Number implements Comparable {
         public function compareTo(Number $other): int { return $this <=> 
$other; }
     }

Without `never`, the `$other` parameter in the interface would need to 
be `mixed` or untyped, preventing the method in the `Number` class from 
adding the type to the engine-enforced signature, requiring it to check 
manually inside the method body.

To me this is another good example of how a small engine change can 
improve the safety of the language for all users, even when third party 
static analysis tools are required to make full use of it.

Best regards
Tim Düsterhus