Trip Report: C++ Standards Committee Meeting in Rapperswil, June 2014 -- Botond Ballo

By Blog Staff | Jul 21, 2014 11:03 AM | Tags: None

Here's one participant's view of the recent standards meeting with some interesting personal perspective.

Trip Report: C++ Standards Committee Meeting in Rapperswil, June 2014

by Botond Ballo

From the article:

Last [month] I attended another meeting of the ISO C++ Standards Committee in Rapperswil, Switzerland (near Zurich). This is the third Committee meeting I have attended; you can find my reports about the previous two here (September 2013, Chicago) and here (February 2014, Issaquah). These reports, particularly the Issaquah one, provide useful context for this post.

With C++14′s final ballot being still in progress, the focus of this meeting was the various language and library Technical Specifications (TS) that are planned as follow-ups to C++14, and on C++17. ...

Post-Rapperswil mailing available

By Blog Staff | Jul 10, 2014 07:00 PM | Tags: None

The post-Rapperswil mailing of new standards papers is now available.

Many of the papers in the mailing have already been published individually on this blog.

NOTE: The following are only those papers in the mailing that have not already been publicized on this blog.

N4109: A proposal to add a utility class to represent expected monad -- R1 -- V Escriba, P Talbot

By Blog Staff | Jul 8, 2014 12:10 PM | Tags: None

A new WG21 paper is available. If you are not a committee member, please use the comments section below or the std-proposals forum for public discussion.

Document number: N4109

Date: 2014-06-29

A proposal to add a utility class to represent expected monad -- Revision 1

by Vicente J. Botet Escriba and Pierre Talbot

Excerpt:

1 History

R1- Revision of N4015 [9] after Rapperswil feedback:

• Switch the expected class template parameter order from expected<E,T> to expected<T,E>.
• Make the unexpected value a salient attribute of the expected class concerning the relational operators.
• Removed open point about making expected<T,E> and expected<T> different classes.

2 Introduction

Class template expected<T,E> proposed here is a type that may contain a value of type T or a value of type E in its storage space. T represents the expected value, E represents the reason explaining why it doesn’t contains a value of type T, that is the unexpected value. Its interface allows to query if the underlying value is either the expected value (of type T) or an unexpected value (of type E). The original idea comes from Andrei Alexandrescu C++ and Beyond 2012: Systematic Error Handling in C++ talk [2]. The interface and the rational are based on std::optional N3793 [5] and Haskell monads. We can consider that expected<T,E> is a generalization of optional<T> providing in addition a monad interface and some specific functions associated to the unexpected type E. It requires no changes to core language, and breaks no existing code.

N4110: Exploring the design space of contract specifications for C++ -- J. Daniel Garcia

By Blog Staff | Jul 7, 2014 03:33 PM | Tags: None

A new WG21 paper is available. If you are not a committee member, please use the comments section below or the std-proposals forum for public discussion.

Document number: N4110

Date: 2014-07-06

Exploring the design space of contract specifications for C++

by J. Daniel Garcia

Excerpt:

This paper explores the design space for introducing contracts as part of the interface of functions and types. The goal is to address the problem of specifying an interface (with special attention to standard library interfaces) making a clear distinction between a contract violation and an explicitly thrown exception. Preconditions and postconditions are attached to function declarations (i.e. to interfaces) rather than to denitions, and are, in principle, checked before and after a function's denition is entered. No macros are needed.

N4121: Compile-Time String: std::string_literal<n> -- Andrew Tomazos

By Blog Staff | Jul 7, 2014 10:37 AM | Tags: None

A new WG21 paper is available. If you are not a committee member, please use the comments section below or the std-proposals forum for public discussion.

Document number: N4121

Date: 2014-07-04

Compile-Time String: std::string_literal<n>

by Andrew Tomazos

Excerpt:

We propose the addition of a class template std::string_literal<n> to the LFTS (and eventually merged into the Strings Standard Library) for the purposes of working with text at compiletime.

The proposed template is a pure library helper class and does not require core language changes or compiler support.

This proposal is depended upon and is blocking N3815 > N4027 > N4113 (Reflection Type Traits) from SG7, which needs to produce compiletime text for reflection of entity names.

N4095-97: File System TS Issues Lists -- Beman Dawes

By Blog Staff | Jul 7, 2014 09:01 AM | Tags: None

A new WG21 paper is available. A copy is linked below, and the paper will also appear in the next normal WG21 mailing. If you are not a committee member, please use the comments section below or the std-proposals forum for public discussion.

Document numbers: N4095-97

Date: 2014-07-05

File System TS Active Issues List (Revision R2)

File System TS Closed Issues List (Revision R2)

File System TS Defect Report List (Revision R2)

by Beman Dawes

4098-99: File System TS Working Draft and Editor's Report -- Beman Dawes

By Blog Staff | Jul 7, 2014 08:44 AM | Tags: None

New WG21 papers are available. If you are not a committee member, please use the comments section below or the std-proposals forum for public discussion.

Document number: N4098-99

Date: 2014-07-05

File System TS Editor's Report, Post-Rapperswil

Working Draft, Technical Specification — File System

by Beman Dawes

Excerpt:

N4099 is the latest File System TS Working Draft. It contains the changes to the File System TS working paper as directed by the committee at the Rapperswil meeting. It also contains editorial changes not requiring committee approval. Details of the changes are listed below.

N4074: Let return{expr} Be Explicit, Revision 2 -- Herb Sutter

By Blog Staff | Jul 7, 2014 07:08 AM | Tags: None

A new WG21 paper is available. A copy is linked below, and the paper will also appear in the next normal WG21 mailing. If you are not a committee member, please use the comments section below or the std-proposals forum for public discussion.

Document number: N4074

Date: 2014-07-02

Let return{expr} Be Explicit, Revision 2

by Herb Sutter

Excerpt:

This paper is a followup to N4029 to follow EWG preference for a variation on that proposal, namely allowing explicit constructors to be called by the syntax return {expr};, with the same semantics as initializing a local variable using return_type var{expr};. This addresses EWG issue #114.

Thanks to Richard Smith for his assistance with the proposed wording. Thanks to Peter Dimov, Gabriel Dos Reis, Howard Hinnant, Stephan T. Lavavej, Mike Miller, Bjarne Stroustrup, Ville Voutilainen, Jona-than Wakely and all others who provided comments on this topic and/or drafts of this paper.

Trip Report: Summer ISO C++ meeting

By H Sutter | Jul 3, 2014 07:43 PM | Tags: None

The summer 2014 WG21 (ISO C++) meeting was held in Rapperswil, Switzerland on June 16-21. Many thanks to HSR Hochschule für Technik Rapperswil for hosting us!

The meeting proceeded pretty much as usual, but because the final (we hope) approval ballot for C++14 itself is still in progress until August 15, in accordance with ISO rules we didn’t formally approve any edits to the C++ working paper. At the next meeting we expect to approve the work of this meeting and next meeting in one batch to kick off the road to C++17.

We also made good progress on most of the eight (8) Technical Specifications in flight; see the current ISO C++ status page for the list. Here are some highlights.

First, we sent three documents out for ballot. This is the first time in ISO C++ history that we have sent three documents out for ballot out of a single meeting.

• File System TS progresses to its final ballot (DTS): We finished addressing the international review comments on the File System comment ballot (aka PDTS), so we now have what should be the final text of the TS. In the next week or two I’ll send that out for its final ballot, and barring surprises we expect the TS to be published this year. Thanks very much to project editor Beman Dawes and the many participants and international reviewers who made this a high quality document!
• Parallelism TS progresses to its main comment ballot (PDTS): This is the "Parallel STL" TS that adds parallel and vector lane execution to STL algorithms.
• Library Fundamentals TS progresses to its main comment ballot (PDTS): We approved adding several features to the Library Fundamentals TS, notably the generalized negator not_fun and fixes for optional<T>. With this, the feature set of “version 1” of the TS is now complete and so it’s going out for its main international review ballot. (But wait, there’s more; see below.)

But we did other things too:

• Library Fundamentals TS “version 2” kicked off: We also approved adding the first items for “version 2” of the Library Fundamentals TS. If you’re wondering how we can do that while version 1 is still in progress, the way to think of this is that we’ve now “finished loading the train” for the feature set of Library Fundamentals TS version 1, and we now will get a round of international comments to fine-tune those features and tighten down the load so the train can start moving out of the station. But while that’s happening, over on the next track we’ve also pulled up another set of empty cars and “started loading the next train” by also approving the creation of the first working paper for the next Library Fundamentals TS, “version 2,” and voting the first items into that. If this were software, we’d call it pipelining – same pattern.
• Networking TS ‘rebooted’: This TS took a big step forward. In recent meetings, the focus of the work had been very small – basically just network byte order conversion, IP addresses, and URIs. At this meeting, the Library Evolution group decided that they would like to make a big bet here and not just take small things piecemeal, but adopt a large and complete proposal based on Boost.ASIO as a starting point. We expect to see an updated version of the ASIO proposal at the next meeting, and hopefully be able to adopt it as our working paper there.
• Concurrency TS: The executors proposal has been improving with work between meetings, but still does not quite have consensus. So at this meeting we have removed executors from the Concurrency TS so that this doesn’t stand in the way of progressing the core parts that do have consensus. It’s possible that executors may be reintroduced before version 1 of the TS, but we’ll see. It’s possible that this TS may be ready for its main international comment ballot (PDTS) after the next meeting, but again we’ll have to see.
• Concepts TS: This got a very thorough wording review by the Core language working group, and we expect it to be in great shape for sending out for PDTS (comment) ballot after our next meeting this fall.

There’s more, but those are some highlights.

In my previous trip report, I wrote:

WG21 has now shipped out documents for ballot in the last three consecutive ISO C++ meetings, and the plan is for this to continue. We have been filling up our pipeline, and now we’re seeing work come out the other end at a brisk pace.

After the long and “working relatively invisibly” period of C++0x, it’s very interesting to see ISO C++ now in a mode where “shipping something out for ISO ballot” is becoming the normal outcome of every meeting. Thanks again to all the volunteers who make it possible! And stay tuned for more to come throughout this year…

This time, again, we sent out not one but three documents for ballot. Quite a meeting.

Thanks, again, to everyone who worked so hard to make this happen.

N4080: File System TS Immediate Issues for Rapperswil -- Beman Dawes

By Blog Staff | Jul 3, 2014 05:35 PM | Tags: None

This paper was approved at the June ISO C++ meeting.

A new WG21 paper is available. A copy is linked below, and the paper will also appear in the next normal WG21 mailing. If you are not a committee member, please use the comments section below or the std-proposals forum for public discussion.

Document number: N4080

Date: 2014-06-20

File System TS Immediate Issues for Rapperswil

by Beman Dawes