Document number: N3709

Date: 2013-08-29

Minutes for July 2013 Santa Clara SG1 Meeting

by Jared Hoberock, Alasdair Mackintosh, Hans Boehm

This meeting took place July 25-26, in Santa Clara, CA. We thank Nvidia for hosting the meeting.

Document number: N3722

Date: 2013-08-30

Resumable Functions

by Niklas Gustafsson, Deon Brewis, Herb Sutter, Sana Mithani

While presenting a proposal that can be adopted or rejected in isolation, this document is related to N3721. The reader is advised to read both as a unit and to consider how the two build on each other for synergy. Reading them in their assigned numeric order is strongly advised.

New in this version: proposed wording for a TS, including language to generalize its applicability to other types than future/shared_future; a section on a possible extension to include generator functions; going back to use of the word ‘resumable’ instead of ‘async’ as the syntactic marker of resumable functions.

Document number: N3721

Date: 2013-08-30

Improvements to std::future and Related APIs

by Niklas Gustafsson, Artur Laksberg, Herb Sutter, Sana Mithani

This proposal is an evolution of the functionality of std::future/std::shared_future. It details additions which can enable wait free compositions of asynchronous operations.

This document supersedes N3634: the title has been changed, and the proposed changes have been modified to be expressed as edits to the C++ Draft Standard.

New in this version: implicit unwrapping (one level) of future<future<R>> to future<R> in then().

... C++ suffers an evident deficit of asynchronous operations compared to other languages, thereby hindering programmer productivity. JavaScript on Windows 8 has promises (then, join and any), .NET has the Task Parallel Library (ContinueWith, WhenAll, WhenAny), C#/VB has the await keyword (asynchronous continuations), and F# has asynchronous workflows. When compared to these languages, C++ is less productive for writing I/O-intensive applications and system software. In particular writing highly scalable services becomes significantly more difficult. ...

Document number: N3744

Date: 2013-08-30

Proposing [[pure]]

by Walter Brown

Following significant prior art, this paper proposes a pure attribute to specify that a function
or statement is free of observable side effects.

Document number: N3743

Date: 2013-08-30

Conditionally-supported Special Math Functions for C++14, v2

by Walter Brown

This paper proposes to merge International Standard 29124:2010, “Extensions to the C++
Library to support mathematical special functions,” into C++14 as a conditionally-supported
standard library feature.

Document number: N3742

Date: 2013-08-30

Three <random>-related Proposals, v2

by Walter Brown

This paper proposes (1) to add one function template to <algorithm>, (2) to add a few novice-friendly
functions to <random>, and (3) to deprecate some related <cstdlib> legacy interfaces.
The unifying factor in this tripartite proposal is the entities’ respective connection with the
random number component of the C++11 standard library.

Document number: N3741

Date: 2013-08-30

Toward Opaque Typedefs for C++1Y, v2

by Walter Brown

Although this paper is self-contained, it logically follows our discussion, begun several years ago in
N1706 and continued in N1891, of a feature oft-requested for C++: an opaque typedef, sometimes
termed a strong typedef. The earlier of those works was presented to WG21 on 2004-10-20 during
the Redmond meeting, and the later work was presented during the Berlin meeting on 2005-04-06.
Both presentations resulted in very strong encouragement to continue development of such a
language feature. Alas, the press of other obligations has until recently not permitted us to
resume our explorations.

Now with C++11 as a basis, we return to the topic. Where our earlier thinking and nomenclature
seem still valid, we will repeat and amplify our exposition; where we have new insights, we will
follow our revised thinking and present for EWG discussion a high-level proposal for a C++1Y
language feature to be known as an opaque alias. ...

Document number: N3740

Date: 2013-08-30

A Proposal for the World’s Dumbest Smart Pointer, v2

by Walter Brown

We present the following code as a preliminary specification of intent in order to serve as a
basis for technical discussion. Designed as a pointer that takes no formal notice of its pointee’s
lifetime, this not-very-smart pointer template is intended as a replacement for near-trivial uses of
bare/native/raw/built-in/dumb C++ pointers, especially when used to communicate with (say)
legacy code that traffics in such pointers. It is, by design, exempt (hence its working name) from
any role in managing any pointee, and is thus freely copyable independent of and without regard
for its pointee.

We have found that such a template provides us a standard vocabulary to denote non-owning
pointers, with no need for further comment or other documentation to describe the near-vacuous
semantics involved...

Document number: N3711

Date: 2013-08-15

Task Groups As a Lower Level C++ Library Solution To Fork-Join Parallelism

by Artur Laksberg and Herb Sutter

The task_group concept proposed in this document is based on the common subset of the PPL and the TBB libraries, which also use task_group internally to implement many of their own parallel algorithms. This proposal complements the high-level Parallel STL algorithms proposal [2] by enabling arbitrary fork-join parallelism, including arbitrary additional higher-level parallelism algorithms, to be built in a natural and portable way.

Together with [2], we believe this offers a viable alternative to a language-based proposal for low-level fork-joined parallelism with competitive (or in some cases better) usability, generality, and performance.

Document number: N3716p>

Date: 2013-08-18

A printf-like Interface for the Streams Library (revision 1)

by Zhihao Yuan

Changes since N3506

• Support Boost.Format’s simple positional syntax (%1%, %2% ...).
• Cover the cornor cases “not-mentioned” by the C standard.
• Mention the function style syntax suggested by BSI in “Future Issues”.

Overview

cout << putf("hello, %s\n", "world");

Printf defines the most widely used syntax to format a text output. It exists in C, Perl, Python and even Java™, and is available from Qt to Boost.Format[1], but not C++ standard library. This proposal tries to define such an interface based on the printf function defined by C[2] for the C++ I/O streams library, with the error handling policy and the type safety considered.