WG21 MAILINGS

Mailings

The C++ Committee publishes papers in monthly mailings. Pick one below to browse its papers.

Submit Issue

August 2026 Papers Latest

⧉ open-std.org

48 papers · WG21 mailing

A WG21 mailing is the month's batch of papers under committee review.
Published 2026-07-28
Author(s) Guy Davidson
Audience
Published 2026-07-22
Author(s) Giuseppe D'Angelo
Audience ,
Tracking issue View on GitHub
Abstract Smart pointer classes are universally recognized as the idiomatic way to express ownership of a resource (very incomplete list: [Sutter], [Meyers], [R.20]). On the other hand, raw pointers (and references) are supposed to be used as non-owning types to access a resource.
Published 2026-08-12
Author(s) Barry Revzin, Bruno Cardoso Lopez, Zach Laine, Michael Park
Audience
Revisions R4
Tracking issue View on GitHub
Abstract We propose the addition of a new kind of expression, called a `do` expression. In its simplest form:
Published 2026-08-14
Author(s) Timur Doumler, Joshua Berne
Audience ,
Revisions R7R6
Tracking issue View on GitHub
Abstract In this paper, we enumerate all cases of core language undefined behaviour explicitly specified in the C++ Standard, group them into ten categories, and classify them along a number of relevant criteria.
Published 2026-08-14
Author(s) Zhihao Yuan, Jordan Saxonberg
Audience
Tracking issue View on GitHub
Abstract We propose `unique_ptr` overloads for `std::const_pointer_cast` and `std::dynamic_pointer_cast`. For each kind of cast, we allow users to choose between either using the defaulted deleter or preserving the original deleter type for each kind of cast.
Published 2026-07-27
Author(s) Hewill Kang
Audience , ,
Revisions R3
Tracking issue View on GitHub
Abstract This paper proposes the Tier 1 adaptor `views::slice` (as described in [P2760](https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2023/p2760r1.html)) to enhance the C++29 ranges library. Notably, this is the first standard range adaptor that accepts two arguments — `start` and `end` — to specify the interval [`start`, `end`) for slicing a range.
Published 2026-08-12
Author(s) Yihe Li
Audience
Revisions R4
Tracking issue View on GitHub
Abstract The motivation for this view is given in [P2760R1] and quoted below for convenience:
Published 2026-07-21
Author(s) Yihe Li
Audience
Tracking issue View on GitHub
Abstract The first appearance of the compile-time message parameter in the C++ core language is in C++11, where `static_assert` declaration was introduced into the language by [N1720] with the syntax `static_assert(condition, message)`. At that time, the message parameter was the first time that users of the C++ language were able to control the generation of diagnostic messages in a dynamic way (excluding
Published 2026-06-11
Author(s) Alisdair Meredith
Audience
Tracking issue View on GitHub
Abstract Throwing from an overloaded `delete` operator is undefined behavior, yet `delete` operators have a non-throwing exception specification by default, leading to a deterministic call to `terminate` before any undefined behavior can occur. This paper suggests we can do better than “undefined behavior” for the remaining cases.
Published 2026-08-12
Author(s) Maged Michael, Michael Wong, Paul McKenney, Mark de Wever
Audience
Revisions R7R6R5R4R3
Tracking issue View on GitHub
Abstract This paper proposes extending the C++26 hazard pointer interface to support synchronous reclamation. This revision, P3427R8, revises R7 by following LWG 2026-07-24 feedback. Ready for LWG review.
Published 2025-12-01
Author(s) Gabriel Dos Reis
Audience
Tracking issue View on GitHub
Published 2026-07-28
Author(s) Yehonatan Simian yonisimian@gmail.com, Ran Regev regev.ran@gmail.com
Audience ,
Abstract This proposal introduces an extension to C++ structured bindings, allowing assignment to existing variables.
Published 2026-08-12
Author(s) Victor Zverovich
Audience
Revisions R2R1
Tracking issue View on GitHub
Abstract [P2845], adopted in C++26, added formatting support for `std::filesystem::path`, addressing encoding issues and making formatting of a path as an ordinary (`char`) string lossless except for one case, unpaired surrogates on Windows. This paper proposes addressing this case and making such formatting lossless by default via the WTF-8 encoding ([WTF-8]). This will improve consistency in path handlin
Published 2026-08-09
Author(s) Robert Leahy
Audience ,
Revisions R0
Tracking issue View on GitHub
Abstract The fundamental scope algorithm is `within`. It establishes a scope by running an enter scope sender. Thereafter it allows a child operation to run (in that scope since the exit scope sender has not yet run), and then before completing the overall operation runs the exit scope sender yielded by the enter scope sender.
Published 2026-07-23
Author(s) Giuseppe D'Angelo
Audience ,
Revisions R0
Tracking issue View on GitHub
Abstract In this table we’re summarizing the status quo and the changes brought by the options and extensions illustrated above. The table refers to `std::copy`, but similar changes are expected for the other algorithms of the family.
Intent Inform
Published 2026-08-01
Author(s) Vinnie Falco
Audience
Abstract [SD-4](https://isocpp.org/std/standing-documents/sd-4-wg21-practices-and-procedures) [1] lets the convenor appoint every subgroup chair, set the meeting schedule, and declare consensus.
Intent Inform
Published 2026-08-31
Author(s) Vinnie Falco
Audience
Abstract Ten papers deliver a working profiles prototype covering seventy-seven cases of core-language undefined behavior with zero foundational wording changes, propose five governance correctives drawn verbatim from ISO Directives, and document how
Published 2026-07-21
Author(s) Yihe Li
Audience
Revisions R0
Tracking issue View on GitHub
Abstract Current inconsistency in the `std::ranges::search` API forces users to exit the Ranges world to use searchers and resort to using traditional STL algorithms instead, which is undesirable.
Published 2026-08-12
Author(s) Bjarne Stroustrup
Audience ,
Revisions R1R0
Tracking issue View on GitHub
Abstract The initialization profile should be the easiest to define, but there can be no profile that everybody can agree on without discussion and alternative choices. Also, the rules for initialization and uninitialized memory are far more complex than most people are willing to believe. The initialization profile is foundational to just about every profile, so the initialization profile must isolate tho
Intent Inform
Published 2026-07-30
Author(s) Vinnie Falco
Audience
Abstract Contracts entered C++26 through procedural moves that broke no rule yet left no record of having reconciled the sustained technical opposition to the design.
Published 2026-08-13
Author(s) Joshua Berne
Audience
Published 2026-08-02
Author(s) Robert Leahy
Audience ,
Revisions R0
Tracking issue View on GitHub
Abstract The coroutine promise protocol shipped in C++20 not only banned `return_void` and `return_value` on the same promise type, but did so in an unusually restrictive manner [1]. Notably the aforementioned manner barred implementing the aforementioned mutual exclusion via mutually exclusive constraints.
Published 2026-08-13
Author(s) Joshua Berne
Audience
Published 2026-07-31
Author(s) Robert Leahy
Audience ,
Revisions R0
Tracking issue View on GitHub
Abstract `std::execution` can be thought of as the realization of the asynchronous analogue of a synchronous function [1][2]. The sender is the function itself (with all arguments selected and applied), the receiver is the channel by which the function communicates with its caller (in the synchronous realm by returning or throwing), and the operation state is the “stack” (i.e. a collection of variables wit
Published 2026-07-19
Author(s) Hewill Kang
Audience , ,
Revisions R0
Tracking issue View on GitHub
Abstract This paper proposes two new range adaptors, `views::take_last` and `views::drop_last`, that respectively produce the last *N* elements of a range and all-but-the-last *N* elements of a range. They mirror the shape of the existing `views::take` / `views::drop` adaptors and fill an obvious gap in the standard range adaptor set.
Intent Ask
Published 2026-08-11
Author(s) Vinnie Falco, Ville Voutilainen
Audience
Revisions R0
Tracking issue View on GitHub
Abstract This paper asks EWG (the Evolution Working Group) to sever an unadopted architecture claim from the wording it is bundled with, so that the wording proceeds and the claim gets its own paper and poll.
Intent Ask
Published 2026-08-10
Author(s) Vinnie Falco
Audience
Revisions R0
Tracking issue View on GitHub
Abstract WG21 sometimes records polls on paper revisions that did not appear in a pre-meeting mailing. When an in-meeting revision changes the design, recording the poll can shift the consensus burden before national body experts have seen the change.
Intent Inform
Published 2026-08-11
Author(s) Vinnie Falco, Ville Voutilainen
Audience
Revisions R0
Tracking issue View on GitHub
Abstract P3100R8 proposes that implicit contract assertions, configured through Contracts evaluation semantics and Labels, control runtime checking of core-language undefined behavior. The Profiles papers, P3589R2 and P3984R0, instead make a Profile the named mechanism that selects and defines such guarantees.
Intent Inform
Published 2026-08-11
Author(s) Vinnie Falco, Ville Voutilainen
Audience
Revisions R0
Tracking issue View on GitHub
Abstract The response space for a throwing implicit contract assertion contains at least eight options, not the four before EWG.
Intent Inform
Published 2026-08-02
Author(s) Vinnie Falco, Ville Voutilainen
Audience
Revisions R0
Tracking issue View on GitHub
Abstract `std::core_ub` (P4317R1) guards the runtime-checkable cases of core-language undefined behaviour and, when enforced, guarantees the check runs. It leaves one question open: after a guarded violation is detected, does the program continue or terminate? This paper answers terminate. Whether contracts are the right substrate for these checks at all is argued against them in P4332R0; this paper takes
Published 2026-08-13
Author(s) Mark Hoemmen, Rob Parolin
Audience
Revisions R0
Tracking issue View on GitHub
Abstract Given an accessor `a` of type `A`, a “const element type version of `a`” (if it exists) is an accessor `b` of a possibly different type `B`, where
Published 2026-07-21
Author(s) Iliya Guterman, Anthony Williams
Audience
Revisions R0
Tracking issue View on GitHub
Abstract As a developer coming from languages other than C++, I grew accustomed to using enums to represent flags. However, such behavior is noticeably absent from the C++ language.
Intent Inform
Published 2026-08-01
Author(s) Vinnie Falco
Audience
Revisions R0
Tracking issue View on GitHub
Abstract P4297R1 [1] asks EWG to sever P3100R8's architecture claim from its case-by-case wording review. This paper demonstrates the severing is feasible.
Intent Inform
Published 2026-08-11
Author(s) Vinnie Falco
Audience
Revisions R0
Tracking issue View on GitHub
Abstract Standardizing a continuing (log-and-continue) response for implicit contract assertions on core-language undefined behavior, as a portable guarantee every implementation carries, returns less than it costs.
Published 2026-08-11
Author(s) Jan Schultke
Audience
Abstract [[P2806R4]](https://wg21%2elink/p2806r4) proposed to let the user omit the last semicolon in a `do` expression to yield a result. This paper argues against that feature for a variety of reasons.
Published 2026-08-14
Author(s) Ville Voutilainen, Ville Voutilainen
Audience
Abstract This paper supplies a design and implementation exploration for a more library-oriented approach to contracts.
Published 2026-06-21
Author(s) Ungureanu Radu-Andrei
Audience
Abstract A parameter declaration may contain a braced-init-list immediately following the `declarator`.
Published 2026-07-29
Author(s) Robert Leahy
Audience ,
Abstract Under the status quo of the C++29 working draft one can write asynchronous code which branches synchronously:
Intent Inform
Published 2026-07-28
Author(s) Vinnie Falco
Audience
Abstract This paper examines select papers that propose to extend P2900 contracts. Each paper is evaluated through two lenses:
Published 2026-07-31
Author(s) John Spicer, Ville Voutilainen, Bjarne Stroustrup, Vinnie Falco, Jose Daniel Garcia Sanchez
Audience , ,
Abstract This document makes one narrow claim: that the mechanism P2900 defines for contract assertions is the wrong mechanism for checks whose purpose is to detect or mitigate core-language undefined behavior, as proposed by P3100. The claim does not depend on any hostile reading of contracts. It follows from what the contracts proposal says about itself: P3846R1 concedes that guaranteed enforcement is a
Published 2026-08-09
Author(s) Bjarne Stroustrup, J-Daniel Garcia, Vinnie Falco, John Spicer, Ville Voutilainen
Audience
Published 2026-08-03
Author(s) Robert Leahy
Audience ,
Abstract Enabled by variadic templates and forwarding references, C++11 brought emplace construction. Containers, wrappers, et cetera could provide variadic constructors or functions which forwarded arguments through to a constructor of some wrapped or contained type thereby creating an instance of that type without intervening temporaries (which would be copied or moved from).
Published 2026-08-03
Author(s) Robert Leahy
Audience ,
Abstract `emplace_from` is a proposed standard library class template which enables emplace functionality (e.g. `std::vector::emplace_back`, `std::optional::emplace`, et cetera) to be used to construct immovable types returned by factory functions (e.g. `std::execution::connect`).
Published 2026-08-11
Author(s) Barry Revzin
Audience
Abstract This is a follow-up to [[P2484R0] (Extending class types as non-type template parameters)](https://wg21.link/p2484r0) and [[P3380R1] (Extending support for class types as non-type template parameters)](https://wg21.link/p3380r1) (the latter of which starts with a useful reading list), and is a new solution to that problem building upon three insights:
Published 2026-08-11
Author(s) Shubham Avasthi
Audience
Abstract Currently, there is no standardized, zero-overhead way to clear the elements of container adaptors. When developers need to reuse a <ins>std::priority_queue or std::queue</ins> in a performance-critical loop, they are forced to use one of two suboptimal workarounds:
Published 2026-08-13
Author(s) Jarrad Waterloo
Audience , ,
Abstract By formalizing `pure alias types`, we remove seeming inconsistencies between references and other alias types. This will result in fewer instances of immediate dangling, return based dangling and superfluous aliasing.
Published 2026-08-14
Author(s) Ville Voutilainen
Audience
Abstract This paper explains how to decouple UB-checks from Contracts. Because multiple people have expressed a desire to look at that. Further, this paper explains how to do that without redefining Undefined Behavior. This paper focuses on *how*. This paper doesn't focus on *why*.
Published 2026-08-12
Author(s) Bjarne Stroustrup
Audience ,
Abstract ```cpp The most important examples involve function calls that pass a pointer to initialized or uninitialized memory. Marking an argument with [[ref_to_uninit]] means that that argument must refer to uninitialized memory. If not, the initialization profile requires that that an argument refers to an initialized object. Consider int x [[uninit]]; using T = decltype(x); // does T accept a pointer to
· source: open-std.org