"Predictable lambdas": Might be pursued (under exploration). Being able to declare a lambda on the stack, without initializing it right away, and having access to its constructor (some sort of placement new on an uninitialized lambda, kind of like an optional<lambda>)

Two comments here:
(1) {{citation needed}}. Every single entry in these tables will benefit from a third column with the URL(s) of people actually requesting these things. Otherwise it's very easy for me to believe that an entry has lost something in translation, and/or is solving an XY problem.

(2) This particular entry probably has an XY problem; but if we assume we really do want to solve Y, then the feature request here doesn't really have anything to do with "lambdas." What it's really asking for is a pair of attributes to stick on a variable: [[no_construct]], to skip the constructor but still destroy the variable at end-of-scope as usual; and [[no_destroy]] to do the constructor but skip the destructor.

Clang and GCC both support [[no_destroy]], but only on static and thread-local storage.

Nobody supports [[no_construct]] yet.

But I know about these attributes because if we had them for stack variables then the vendor could implement P1144 `T std::relocate(T*)` without intimate knowledge of the calling convention:

    template<class T>

    T relocate(T *src) {

      if constexpr (std::is_trivially_relocatable_v<T>) {

        [[do_not_construct]] T dst;

        std::relocate_at(src, &dst);  // construct dst and destroy src, as if by memcpy

        return dst;  // but still get the benefit of NRVO here

      } else {

        T dst = T(std::move(*src));

        std::destroy_at(src);

        return dst;  // get the benefit of NRVO here

      }

    }

The [[no_destroy]] attribute is probably desirable for some SG14 folks, too, because it lets you have a global variable like

    [[no_destroy]] const std::string kConstant = "constant";

of a non-trivial type that requires dynamic initialization, but the programmer doesn't care if its destructor runs at program exit — that's just useless bookkeeping, so we would like to have a way to tell the compiler to omit it.

–Arthur

On Wed, Jul 12, 2023 at 2:39 PM Patrice Roy via SG14 <sg14@lists.isocpp.org> wrote:

As a reminder :)

Le mar. 11 juil. 2023 à 23:34, Michael Wong via SG14 <sg14@lists.isocpp.org> a écrit :

Topic: SG14 Low Latency Monthly This meeting is focused on Finance/Low Latency though we can continue with the Games paper that
was started in January, depending on what other papers or topics are of
interest.

I am also looking for a finance Subgroup chair. Thank you.

Hi,

Michael Wong is inviting you to a scheduled Zoom meeting.

Topic: SG14 monthly
Time: 2nd Wednesdays 02:00 PM Eastern Time (US and Canada)
    Every month on the Second Wed,

Join from PC, Mac, Linux, iOS or Android:
https://iso.zoom.us/j/93151864365?pwd=aDhOcDNWd2NWdTJuT1loeXpKbTcydz09
    Password: 789626

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Agenda:

1. Opening and introduction

ISO Code of Conduct
<
https://isotc.iso.org/livelink/livelink?func=ll&objId=20882226&objAction=Open&nexturl=%2Flivelink%2Flivelink%3Ffunc%3Dll%26objId%3D20158641%26objAction%3Dbrowse%26viewType%3D1
*>*

ISO patent policy.
https://isotc.iso.org/livelink/livelink/fetch/2000/2122/3770791/Common_Policy.htm?nodeid=6344764&vernum=-2

IEC Code of Conduct:

https://www.iec.ch/basecamp/iec-code-conduct-technical-work

WG21 Code of Conduct:

https://isocpp.org/std/standing-documents/sd-4-wg21-practices-and-procedures

1.1 Roll call of participants

1.2 Adopt agenda

1.3 Approve minutes from previous meeting, and approve publishing
 previously approved minutes to ISOCPP.org

1.4 Action items from previous meetings

2. Main issues (125 min)

2.1 General logistics

Varna F2F

C++23 and C++26 status

Future meeting plans

*Mar 8, 2023 02:00 PM ET: Embedded

*Apr 12, 2023  02:00 PM ET: Cancelled

* May 10, 2023  02:00 PM ET: Cancelled

* June 14, 2023  02:00 PM ET: Cancelled

* July 12, 2023  02:00 PM ET: Finance

* Aug 9, 2023  02:00 PM ET: Games

* Sep 12, 2023  02:00 PM ET: Embedded

* Oct 1: CPPCON

* Oct 10, 2023  02:00 PM ET: Finance

*Nov 8, 2023  02:00 PM ET: Kona F2F Cancelled

* Dec 12, 2023  02:00 PM ET: Games

2.2 Paper reviews
Discussion on Embedded:
Review latest mailings:
P2532 Removing exception_ptr from the receivers concept
Based on the last meeting and the discussions here.
P2544 C++ Exceptions are becoming more and more problematic
We might want to chime in here.
/Paul
P. S. P2327 de-deprecating volatile received a "consensus" straw poll.


Discussion on Low Latency/Finance topics

http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2022/p1839r4.pdf

Patrice's paper on games.

P2300
Swift



Discussion about Games topics:

 P2388R1 - Minimum Contract Support: either Ignore or Check_and_abort
<http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2021/p2388r1.html>

Patrice's WIP on Games issues.

Finance topics from July 14, 2021.

https://lists.isocpp.org/sg14/2021/06/0636.php

https://lists.isocpp.org/sg14/2021/07/0642.php

2.2.1 any other proposal for reviews?

Deterministic Exception for Embedded by James Renwick
https://www.pure.ed.ac.uk/ws/portalfiles/portal/78829292/low_cost_deterministic_C_exceptions_for_embedded_systems.pdf

Freestanding?

SG14/SG19 features/issues/defects:

https://docs.google.com/spreadsheets/d/1JnUJBO72QVURttkKr7gn0_WjP--P0vAne8JBfzbRiy0/edit#gid=0

2.3 Domain-specific discussions

2.3.1 SIG chairs

   - Embedded Programming chairs: Ben Craig, Wouter van Ooijen and Odin
 Holmes, John McFarlane

   - Financial/Trading chairs: Staffan TjernstrÃm
Carl Cooke, Neal Horlock,
   - Games chairs: Rene Riviera, Guy Davidson and Paul Hampson, Patrice Roy

   - Linear Algebra chairs: Bob Steagall, Mark Hoemmen, Guy Davidson

2.4 Other Papers and proposals

2.5 Future F2F meetings:

2.6 future C++ Standard meetings:
https://isocpp.org/std/meetings-and-participation/upcoming-meetings

-

3. Any other business
Reflector
https://lists.isocpp.org/mailman/listinfo.cgi/sg14
As well as look through papers marked "SG14" in recent standards committee
paper mailings:
http://open-std.org/jtc1/sc22/wg21/docs/papers/2015/
http://open-std.org/jtc1/sc22/wg21/docs/papers/2016/

Code and proposal Staging area
https://github.com/WG21-SG14/SG14
4. Review

4.1 Review and approve resolutions and issues [e.g., changes to SG's
working draft]

4.2 Review action items (5 min)

5. Closing process

5.1 Establish next agenda

5.2 Future meeting


*Mar 8, 2023 02:00 PM ET: Embedded

*Apr 12, 2023  02:00 PM ET: Cancelled

* May 10, 2023  02:00 PM ET: Cancelled

* June 14, 2023  02:00 PM ET: Cancelled

* July 12, 2023  02:00 PM ET: Finance

* Aug 9, 2023  02:00 PM ET: Games

* Sep 12, 2023  02:00 PM ET: Embedded

* Oct 1: CPPCON

* Oct 10, 2023  02:00 PM ET: Finance

*Nov 8, 2023  02:00 PM ET: Kona F2F Cancelled

* Dec 12, 2023  02:00 PM ET: Games

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