RFC: First Class Callables in constant expressions

Hi

Volker and I would like to start discussion on our RFC to support "First
Class Callables in constant expressions".

Please find the following resources for your reference:

• RFC: https://wiki.php.net/rfc/fcc_in_const_expr

• Implementation: https://github.com/php/php-src/pull/17213

• The related "Support Closures in constant expressions" RFC:
  https://wiki.php.net/rfc/closures_in_const_expr

• The "Support Closures in constant expressions" discussion:
  https://externals.io/message/125872

Best regards
Tim Düsterhus

I don't know how to interpret the radio silence from the list, but this
seems like an obvious and good follow-on to the previous RFC and has my
support.

--Larry Garfield

Ship it.
Fin.
;)

Arvīds Godjuks
+371 26 851 664
arvids.godjuks@gmail.com
Telegram: @psihius https://t.me/psihius

Hi

Am 2025-01-31 00:58, schrieb Larry Garfield:

I don't know how to interpret the radio silence from the list, but this
seems like an obvious and good follow-on to the previous RFC and has my
support.

We also interpreted the lack of responses as “this is an obvious
follow-up and I don't have any questions or concerns”, especially since
FCC support also came up in the discussion of the Closure RFC and was
split into a separate RFC primarily to give each of these features the
proper attention with regard to implementation and edge cases. In
hindsight this was the correct decision, since the implementation for
FCC was much more complicated and edge-casey than initially expected,
whereas Closures were reasonably straight forward.

Best regards
Tim Düsterhus

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