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To: mweierophinney@gmail.com
Cc: internals@lists.php.net
Subject: Re: [PHP-DEV] RFC proposal: Invokable interface
Date: Sun, 05 Apr 2026 02:57:49 +0000
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From: hanskrentel@yahoo.de (Hans Krentel)

On Thursday 02 April 2026 16:23:03 (+02:00), Matthew Weier O'Phinney wrote:

 > If you define mixed, you cannot have a void or never return.

We can't speak for Liskov (only she can), but as far as stable PHP is 
concerned never is actually fine, and should also stand a common 
interpretation of LSP, as never is the bottom type and henceforth a 
specialization of mixed. (Some may go for void, too, but that is far more 
abstract and does not work conceptually in PHP if I'm not mistaken.)

Furthermore, the PHP runtime also guarantees that any function can never 
return, not only by the never return type.

So it's at least irrelevant to implement a new throwable via an invocable 
mixed interface or never, the invocation in the runtime guarantees the 
higher contract to the return:

     <?php
     
     interface invocable {
         public function __invoke(): mixed;
     }
     
     $o = new class implements invocable {
         public function __invoke(): never {}
     };
     
     $o();

Interface violation normally yields a compile error, not a type error, 
nowadays.

So if you think that is an error, the discussion should have brought 
something to the table.

-- hakre