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Date: Wed, 05 Feb 2025 13:17:03 +0100
To: Rob Landers <rob@bottled.codes>
Cc: php internals <internals@lists.php.net>, Volker Dusch
 <volker@tideways-gmbh.com>
Subject: Re: [PHP-DEV] RFC: First Class Callables in constant expressions
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References: <2eba1ea4cffa751e6a5f325b972e86b5@bastelstu.be>
 <9d2d54af-f705-4c74-baae-d05d09a1f1e9@app.fastmail.com>
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From: tim@bastelstu.be (=?UTF-8?Q?Tim_D=C3=BCsterhus?=)

Hi

Am 2025-02-02 15:35, schrieb Rob Landers:
> My only concern with the RFC is something a bit silly. If I understand 
> correctly, this will be a constant expression:

You understood that correctly.

> It is an incredibly small inconsistency (imho), but other than that, 
> ship it.

I wouldn't call it an inconsistency, it's natural that the allowed 
expressions in a constant-expression context are limited. This 
limitation is mentioned in the second bullet point of the “Constraints” 
section: Only the "basic form" of first-class callables is supported, 
mainly to keep the implementation simple, due to the limited usefulness 
of the more complex function call variants when limited to 
constant-expressions. As an "escape hatch", it's always possible to 
wrote a proper closure that just forwards the calls to the desired 
method.

It will also result in a useful error message that is consistent with 
dynamic new-expressions within const-expr context:

     Fatal error: Cannot use dynamic function name in constant expression 
in test5.php on line 3

and for new-expressions:

     $ cat test5.php
     <?php

     const Foo = new (Foo)();
     $ sapi/cli/php test5.php

     Fatal error: Cannot use dynamic class name in constant expression in 
test5.php on line 3

Best regards
Tim Düsterhus