WG21 MAILINGS

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

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April 2026 Papers

⧉ open-std.org

138 papers · WG21 mailing

A WG21 mailing is the month's batch of papers under committee review.
Intent Informational
Published 2026-03-03
Author(s) Guy Davidson
Audience
Abstract | Replaces: | | | 5035 | | --- | --- | --- | --- | | Date: | | | 2026-03-03 | | Reply to: | | | Guy Davidson (standard.guy@hatcat.com) |
Intent Informational
Published 2026-03-09
Author(s) Braden Ganetsky
Audience
Abstract There will be about 6 meeting rooms in Croydon, 4 of which will be occupied all week long by the usual suspects. There is a “meeting rooms” wiki page. An email has been sent to ask that every subgroup chair requests meeting room space and time there. So far only 4 study groups have requested space and time. The rooms will be distributed based on those who registered. Anyone who is late will not ha
Intent Informational
Published 2026-04-17
Author(s) Braden Ganetsky
Audience
Abstract Nina Ranns presents. Every participant is responsible for understanding and abiding by the following documents. It is assumed that every participant has read them before attending this meeting.
Intent Informational
Published 2026-04-08
Author(s) Guy Davidson
Audience
Intent Proposal
Published 2026-04-13
Author(s) Guy Davidson
Audience
Revisions R7
Tracking issue View on GitHub
Intent Proposal
Published 2026-03-27
Author(s) JeanHeyd Meneide
Audience , ,
Tracking issue View on GitHub
Abstract > I’m very keen on std::embed. I’ve been hand-embedding data in executables for NEARLY FORTY YEARS now. — Guy "Hatcat" Davidson, June 15, 2018
Intent Proposal
Published 2026-03-27
Author(s) JeanHeyd Meneide
Audience ,
Tracking issue View on GitHub
Abstract The only way to declare a dependency in C++ currently is to use a `#include` statement. With Modules coming to C++, dependency information was greatly enhanced by preambles and globule module fragments which allow for both the compiler and build system to understand physical and semantic layout of code. However, there is still a problem area that C++ has not addressed that people in the brave new
Intent Proposal
Published 2026-03-23
Author(s) Ryan McDougall, Lakshay Garg
Audience
Tracking issue View on GitHub
Abstract Type erased callables like `std::move_only_function` are the backbone of most asynchronous systems. Users of such systems close their operations in lambdas and place them in a concurrent queue to be processed elsewhere. Performance is often key in such systems, and such operations may want its own local reusable scratch memory. Or perhaps an accumulator for hysteresis over multiple calls.
Intent Informational
Published 2026-04-17
Author(s) Mungo Gill, Vinnie Falco
Audience
Revisions R2R1R0
Tracking issue View on GitHub
Abstract C++20 provides symmetric transfer ([P0913R1](http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2018/p0913r1.html)[1]) - a mechanism where `await_suspend` returns a `coroutine_handle<>` and the compiler resumes the designated coroutine as a tail call. Coroutine chains execute in constant stack space. `std::execution`
Intent Proposal
Published 2026-03-23
Author(s) Daniel Towner, Ruslan Arutyunyan
Audience
Revisions R2
Tracking issue View on GitHub
Abstract ISO/IEC 19570:2018 introduced data-parallel types to the C++ Extensions for Parallelism TS [P1928R15]. That paper, and several ancillary papers, do an excellent job of setting out the main features of an extension to C++ which allows generic data parallel programming on arbitrary targets. However, it is inevitable that the programmer will want to make some use of target-specific intrinsics in orde
Intent Proposal
Published 2026-03-30
Author(s) Daniel Towner, Ruslan Arutyunyan
Audience
Tracking issue View on GitHub
Abstract The Working Draft of C++26 includes data parallel types. It mostly provides operators which work on or with `std::simd` types, but it also includes overloads of useful functions from other parts of C++ (e.g., sin, cos, abs). In [P0543R3] a proposal was made to provide saturating operation support for some basic arithmetic operations and casts. In particular, `saturating_add`, `saturating_sub`, `sa
Intent Proposal
Published 2026-03-20
Author(s) Daniel Towner, Ruslan Arutyunyan
Audience ,
Revisions R2
Tracking issue View on GitHub
Abstract The C++ standard library includes data-parallel types in the `<simd>` header, currently restricting element types to a closed list: arithmetic types and `std::complex` specializations. This paper proposes a minimal change to the specification in which the closed list is replaced with trait-based constraints that handle all existing types while naturally extend support to enumerations, `std::byte`
Intent Proposal
Published 2025-03-26
Author(s) Hewill Kang
Audience ,
Tracking issue View on GitHub
Abstract This paper provides the `at()` method to `ranges::view_interface` to provide a safe access method for the view class. Revision history R2 Rename the feature-test macro based on LEWG feedback. R1 Added wording for freestanding. R0 Initial revision. Discussion Currently, the committee adopted [P2821](https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2023/p2821r4.html) in C++26, which adds a missin
Intent Proposal
Published 2026-03-23
Author(s) Hewill Kang
Audience ,
Tracking issue View on GitHub
Abstract The exposure of user-defined constructors for iterators/sentinels in `<ranges>` currently does not follow consistent rules, which is reflected in the fact that some of them are public and some are private. This paper disables their visibility to comply with best practices.
Intent Proposal
Published 2026-03-30
Author(s) Elias Kosunen
Audience
Tracking issue View on GitHub
Intent Proposal
Published 2026-04-12
Author(s) Tiago Freire
Audience
Tracking issue View on GitHub
Abstract Addition and uniformization of integer arithmetic functions with overflow behavior
Intent Proposal
Published 2026-04-16
Author(s) Nicolas Morales, Christian Trott, Mark Hoemmen, Damien Lebrun-Grandie
Audience
Tracking issue View on GitHub
Abstract C++23 introduced `mdspan` ([[P0009R18]](https://wg21.link/p0009r18)), a non-owning multidimensional array abstraction that has a customizable layout. Layout customization was originally motivated in [[P0009R18]](https://wg21.link/p0009r18) with considerations for interoperability and performance, particularly on different architectures. Moreover, [[P2630R4]](https://wg21.link/p2630r4) introduced `
Intent Proposal
Published 2026-03-27
Author(s) Robert Leahy
Audience
Revisions R3R2
Tracking issue View on GitHub
Abstract In broad terms a regular (i.e. synchronous) function call has access to two forms of storage throughout its lifetime (note that the “lifetime” of a regular function call is the time between the call thereto and the return therefrom):
Intent Proposal
Published 2025-03-21
Author(s) Jeremy Rifkin
Audience
Tracking issue View on GitHub
Abstract The `__COUNTER__` predefined macro is a common language extension for C and C++ which expands to an integer literal that starts at `0` and increments by `1` every time it is expanded in a translation unit. This is useful for generating unique identifiers, generating unique indices, and other preprocessor metaprogramming uses.
Intent Proposal
Published 2026-03-26
Author(s) Maged Michael, Michael Wong, Paul McKenney, Mark de Wever
Audience
Tracking issue View on GitHub
Abstract This paper proposes extending the working draft (N5008) C++26 hazard pointer interface to support synchronous reclamation. The R1 revision of this paper was reviewed by SG1 in Wroclaw 2024 and forwarded to LEWG with feedback "The word 'asynchronous' doesn't belong in the name of the free function". This revision, P3427R2, revises R1 by following SG1 feedback.
Intent Proposal
Published 2026-03-23
Author(s) Daniel Towner
Audience
Revisions R2
Tracking issue View on GitHub
Abstract When iterating over large dynamic data sets using `std::simd` there will inevitably be situations where the very last block of data doesn’t fill the entire `std::simd` object. This remainder needs to be processed using a partially filled `std::simd` object. For example:
Intent Proposal
Published 2026-02-27
Author(s) Barry Revzin
Audience
Tracking issue View on GitHub
Abstract In [[P2641R4]](https://wg21.link/p2641r4), I proposed adding the metafunction
Intent Proposal
Published 2026-04-19
Author(s) Joshua Berne, Timur Doumler, Jens Maurer, Shafik Yaghmour
Audience
Revisions R0
Tracking issue View on GitHub
Intent Proposal
Published 2026-03-26
Author(s) Joshua Berne
Audience
Tracking issue View on GitHub
Intent Proposal
Published 2026-03-02
Author(s) Nikita Sakharin
Audience ,
Tracking issue View on GitHub
Abstract This paper proposes to add an `isqrt` function (template) to calculate the integer square root of a nonnegative integer. Mathematically defined as:
Intent Proposal
Published 2026-04-07
Author(s) Michael Florian Hava
Audience
Tracking issue View on GitHub
Intent Proposal
Published 2026-03-03
Author(s) Jan Schultke
Audience
Tracking issue View on GitHub
Abstract **Intuition**: "carry-less" means we use XOR instead of plus.
Intent Proposal
Published 2025-10-05
Author(s) Peter Bindels, Hana Dusikova, Jeremy Rifkin, Marco Foco, Alexey Shevlyakov
Audience ,
Tracking issue View on GitHub
Abstract We propose a standard string view type that guarantees null-termination.
Intent Proposal
Published 2026-03-30
Author(s) Paul E. McKenney, Alan Stern, Michael Wong, Maged Michael, Gonzalo Brito
Audience
Tracking issue View on GitHub
Abstract * P3692R4 updates the C++ working draft to N5032 and applies feedback from CWG. It also adds a citation to the NVIDIA PTX prohibition against OOTA.
Intent Proposal
Published 2026-03-24
Author(s) Nicolai Josuttis
Audience ,
Revisions R2
Tracking issue View on GitHub
Abstract Using filter views is both risky and non-intuitive. Let us look at some typical use cases.
Intent Proposal
Published 2026-03-26
Author(s) Barry Revzin, Tomasz Kamiński
Audience ,
Tracking issue View on GitHub
Abstract [[P3074R7] (trivial `union`s (was `std::uninitialized<T>`))](https://wg21.link/p3074r7) was adopted in Hagenberg. One of the goals of that paper was to make an example like this work:
Intent Proposal
Published 2026-03-26
Author(s) Ruslan Arutyunyan, Mark Hoemmen, Alexey Kukanov, Bryce Adelstein Lelbach, Abhilash Majumder
Audience ,
Tracking issue View on GitHub
Abstract We propose `ranges` algorithm overloads (both parallel and non-parallel) for the `<numeric>` header.
Intent Proposal
Published 2026-03-27
Author(s) Lauri Vasama
Audience
Tracking issue View on GitHub
Abstract [P3492R2] was forwarded to CWG in Hagenberg. In addition to its main language additions, it provided a drive-by fix for the poorly specified selection of deallocation functions in placement new expressions. The wording changes were split into this paper to make it easier to review the changes happening concurrently in this area:
Intent Proposal
Published 2026-04-10
Author(s) Michael Florian Hava
Audience
Tracking issue View on GitHub
Intent Proposal
Published 2026-03-24
Author(s) Giuseppe D'Angelo, Ruslan Arutyunyan
Audience ,
Revisions R1
Tracking issue View on GitHub
Abstract In the Tokyo 2024 meeting [P2248R8] (Enabling list-initialization for algorithms) was adopted.
Intent Proposal
Published 2026-03-26
Author(s) Barry Revzin
Audience ,
Revisions R1
Tracking issue View on GitHub
Abstract At the Sofia meeting, [[P2996R13] (Reflection for C++26)](https://wg21.link/p2996r13), [[P3394R4] (Annotations for Reflection)](https://wg21.link/p3394r4), [[P3293R3] (Splicing a base class subobject)](https://wg21.link/p3293r3), [[P3491R3] (`define_static_{string,object,array}`)](https://wg21.link/p349143), [[P3096R12] (Function Parameter Reflection in Reflection for C++26)](https://wg21.link/p30
Intent Proposal
Published 2026-03-26
Author(s) Lucian Radu Teodorescu, Ruslan Arutyunyan
Audience
Tracking issue View on GitHub
Abstract `parallel_scheduler` [[P2079R10](https://wg21.link/p2079r10)] was a long time in the making and was it adopted in Sofia 2025; still more design concerns were raised after that. This paper proposes to iterate on some of these aspects, aiming to achieve the best possible outcome from `parallel_scheduler`.
Intent Proposal
Published 2026-03-26
Author(s) Eric Niebler
Audience , ,
Revisions R4R3
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Intent Proposal
Published 2026-03-07
Author(s) Nicolai Josuttis
Audience
Tracking issue View on GitHub
Abstract Nicolai Josuttis: P3828R1: Rename the to_input view to as_input
Intent Proposal
Published 2026-04-01
Author(s) Ted Lyngmo
Audience ,
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Abstract C++11 introduced `std::lock` and `std::try_lock` (and C++17 introduced `std::scoped_lock`) to simplify deadlock-free acquisition of multiple lockables. These algorithms support *BasicLockable* and *Lockable* objects, but there is currently no facility for timed acquisition of multiple *TimedLockable* objects.
Intent Proposal
Published 2026-04-16
Author(s) Ted Lyngmo
Audience ,
Revisions R1
Tracking issue View on GitHub
Abstract This paper proposes `std::multi_lock`, a RAII class template that combines the functionality of `std::unique_lock` and `std::scoped_lock`. Unlike `std::scoped_lock`, which provides only basic RAII semantics, `std::multi_lock` offers the full flexibility of `std::unique_lock` (deferred locking, try-lock operations, timed locking, and ownership transfer) while supporting multiple mutexes simultaneou
Intent Proposal
Author(s) Mateusz Pusz
Audience , , ,
Tracking issue View on GitHub
Intent Proposal
Published 2026-03-26
Author(s) Ville Voutilainen
Audience ,
Revisions R1
Tracking issue View on GitHub
Abstract The papers [P3818](https://open-std.org/JTC1/SC22/WG21/docs/papers/2025/p3818r1.html) and [P3820](https://open-std.org/JTC1/SC22/WG21/docs/papers/2025/p3820r1.html) explain the background of the problem we have making uncaught_exceptions() and current_exception(). In short, having those function constexpr is a breaking change in some cases.
Intent Proposal
Published 2025-11-03
Author(s) Timur Doumler, Joshua Berne
Audience
Tracking issue View on GitHub
Abstract [P3835R0], [US 25-052], [FI-071], and [RO 2-056] characterise P2900 as being ‘not safe’ and diminishing the overall ‘safety’ of C++. A central concern is that P2900 provides no method to guarantee *in* *code* that a particular assertion, or all assertions in a given ‘component of a program’, will always be checked. In addition, [RO 2-056] suggests that being able to alter the evaluation semantics
Intent Proposal
Published 2026-03-27
Author(s) Jagrut Dave, Alisdair Meredith
Audience
Revisions R7R6R5R4
Tracking issue View on GitHub
Abstract Several parts of the standard and library refer to structural types, including library mandates that types be structural, yet there is no way to query whether a type is structural. Library mandates clauses mean that library implementers must somehow have this functionality, but it is simply not exposed to users. We propose a new reflection metafunction - *is_structural_type(info)* as a solution, w
Intent Proposal
Published 2026-03-26
Author(s) Christof Meerwald
Audience
Revisions R2R1
Tracking issue View on GitHub
Abstract [CWG 3003](https://cplusplus.github.io/CWG/issues/3003.html) "Naming a deducible template for class template argument deduction" has been raised to clarify that with the current core language wording, class template argument deduction does not work for type template template parameters.
Intent Proposal
Published 2025-03-03
Author(s) Jan Schultke
Audience
Tracking issue View on GitHub
Abstract - C++ supports integer division with rounding towards zero - many other rounding modes are useful:
Intent Proposal
Published 2026-03-25
Author(s) Jan Schultke, Matthias Kretz
Audience
Revisions R1
Tracking issue View on GitHub
Abstract The current specification of floating-point overflow is unclear. Floating-point overflow occurs when finite operands are used as operands, and the result cannot be represented as a finite value. For [[ISO/IEC 60559:2020]](https://www%2eiso%2eorg/standard/80985%2ehtml) floating-point numbers, this results in infinity.
Intent Proposal
Published 2026-03-23
Author(s) Jan Schultke
Audience
Tracking issue View on GitHub
Intent Proposal
Published 2026-03-27
Author(s) Eric Niebler
Audience , ,
Revisions R1R0
Tracking issue View on GitHub
Intent Proposal
Published 2026-03-26
Author(s) Dietmar Kühl
Audience ,
Revisions R3R2R1
Tracking issue View on GitHub
Abstract There are a few NB comments raised about the way `affine_on` works:
Intent Proposal
Published 2026-03-24
Author(s) Matthias Kretz
Audience
Tracking issue View on GitHub
Abstract ```cpp "int std:: __polyfunc :: _Base_invoker <false , int >:: _S_call_storage < …" jmp [QWORD PTR [rdi]] "int std:: __polyfunc :: _Base_invoker <false , int >:: _S_call_storage < …" mov eax , 2 ret ```
Intent Proposal
Published 2026-03-15
Author(s) Barry Revzin
Audience
Revisions R0
Tracking issue View on GitHub
Abstract The `std::format` approach to formatting offers many significant benefits over the prior `<iostream>`s approach that need not be revisited here. However, `<iostream>` does still have one significant advantage: ordering. It is easy to see at a glance with a long `std::cout` statement which pieces are to be formatted in which order. With `std::format`, as the amount of replacement fields increases,
Intent Proposal
Published 2026-03-25
Author(s) Victor Zverovich
Audience
Revisions R2R1R0
Tracking issue View on GitHub
Abstract [P2918] introduced `std::runtime_format` to allow opting out of compile-time format string checks in `std::format`. Subsequently, [P3391] made `std::format` usable in constant evaluation. As a result, `std::runtime_format` can now be evaluated at compile time, making its name misleading. This paper proposes renaming `std::runtime_format` to `std::dynamic_format` to better reflect its semantics and
Intent Proposal
Published 2026-03-24
Author(s) Zhihao Yuan
Audience
Revisions R0
Tracking issue View on GitHub
Abstract RU-220 calls for allowing skipping indirections when constructing `function_ref` to improve codegen. The proposed change in LWG 4264<sup>[1]</sup> is not strictly an optimization because certain behaviors with and without the change are visible, therefore, need to be made unspecified. This paper (P3961) suggests that, in addition to the change, a subset of the "optimized" cases should be mandated.
Intent Proposal
Published 2026-03-25
Author(s) Matthias Kretz
Audience
Revisions R2R1R0
Tracking issue View on GitHub
Abstract As discussed in [P3948R0], because of language inconsistencies, `std::constant_wrapper` is inconsistently not unwrapping for call and subscript operators whereas all other operators can be found via ADL and the conversion operator implemented in `constant_wrapper`. Looking at `std::`
Intent Proposal
Published 2026-03-24
Author(s) Dietmar Kühl
Audience
Revisions R0
Tracking issue View on GitHub
Abstract There are a few NB comments about `task`’s use of allocators:
Intent Proposal
Published 2026-03-26
Author(s) Barry Revzin, Jonathan Wakely, Tomasz Kamiński
Audience
Revisions R1R0
Tracking issue View on GitHub
Intent Proposal
Published 2026-03-24
Author(s) Tomasz Kamiński, Mark Hoemmen
Audience
Revisions R1R0
Tracking issue View on GitHub
Abstract **Addresses [PL007: Define the extent member of the `strided_slice`](https://github.com/cplusplus/nbballot/issues/816)**
Intent Proposal
Published 2026-03-20
Author(s) Daniel Towner, Ruslan Arutyunyan
Audience , ,
Revisions R0
Tracking issue View on GitHub
Abstract The Working Draft makes `simd` types *trivially copyable types*, which allows `std::bit_cast` operations. However, the object representation is unspecified, making the results implementation-defined.
Intent Proposal
Published 2025-03-24
Author(s) Robert Leahy
Audience
Revisions R0
Tracking issue View on GitHub
Abstract When a sender and receiver are connected the result is an operation state. That operation state, once started, is the locus of an asynchronous operation which, upon completion, must notify its consumer of said completion (§33.3 [exec.async.ops]). The way this notification is accomplished is by sending a completion signal to the receiver provided when connecting the sender and receiver.
Intent Proposal
Published 2026-04-17
Author(s) Vinnie Falco, Mungo Gill, Steve Gerbino
Audience
Revisions R1R0
Tracking issue View on GitHub
Abstract This paper asks the committee to advance the *IoAwaitable* protocol as a standard coroutine execution model.
Intent Proposal
Published 2026-03-25
Author(s) Christof Meerwald
Audience
Revisions R0
Tracking issue View on GitHub
Abstract ```cpp template<typename ... T> char *f(T &...); // #1 template<typename T> int *f(T &&); // #2 int i; auto *p = f(i); ```
Intent Informational
Published 2026-04-17
Author(s) Vinnie Falco, Mungo Gill
Audience
Revisions R1R0
Tracking issue View on GitHub
Abstract `std::execution::task` ([P3552R3](https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2025/p3552r3.html)[1]) had open issues identified by national ballot comments, LWG issues, and published papers. Croydon resolved several. This paper classifies each issue by whether it can be resolved after C++26 ships or whether shipping forecloses the fix, and notes which classified issues were addressed at Cr
Intent Proposal
Published 2026-02-09
Author(s) Daniel Towner
Audience ,
Revisions R0
Tracking issue View on GitHub
Abstract This paper proposes adding funnel shift operations to the C++ standard library. Funnel shifts concatenate two integer values, shift the concatenated result, and extract bits. This is a fundamental primitive bit operation with widespread use across many domains including cryptography, hashing, compression, and pseudo-random number generation.
Intent Proposal
Published 2026-03-24
Author(s) Matthias Kretz
Audience
Revisions R0
Tracking issue View on GitHub
Abstract 1. Novel (no other type in the standard library does this2).
Intent Informational
Published 2026-04-17
Author(s) Vinnie Falco, Mungo Gill
Audience
Revisions R0
Tracking issue View on GitHub
Abstract Every sender algorithm in C++26 - all thirty - explained, demonstrated, and mapped to its plain-C++ equivalent.
Intent Proposal
Published 2026-01-14
Author(s) Jonas Persson
Audience
Revisions R0
Tracking issue View on GitHub
Intent Proposal
Published 2026-03-09
Author(s) Jonathan Grant
Audience
Revisions R1R0
Tracking issue View on GitHub
Abstract `compile_assert()` provides a way to specify constraint predicates that are validated at compile time and reported to the user via a diagnostic. This proposal specifies the syntax but not the method used to determine a constraint failure.
Intent Proposal
Published 2026-04-20
Author(s) Michael Wong, phil Ratzloff
Audience
Revisions R0
Tracking issue View on GitHub
Abstract Here is the standard WG21 Revision History section formatted for your SG19 direction paper. You can place this near the top of the document, typically right after the title and author block.
Intent Proposal
Published 2026-04-20
Author(s) Inbal Levi, Fabio Fracassi, Andreas Weis, Corentin Jabot
Audience
Tracking issue View on GitHub
Abstract In 2026-02, the C++ Library Evolution group conducted a series of electronic decision polls [[P4027R0]](https://wg21.link/P4027R0). This paper provides the results of those polls and summarizes the results.
Intent Proposal
Published 2026-02-26
Author(s) Michael Wong, SG14
Audience
Revisions R0
Tracking issue View on GitHub
Abstract In low-latency finance, different threads (e.g., market data ingestion vs. order execution) must communicate without OS-level locks or blocking.
Intent Proposal
Published 2026-03-24
Author(s) Ruslan Arutyunyan
Audience
Revisions R0
Tracking issue View on GitHub
Abstract This paper proposes to rename `system_context_replaceability` namespace.
Intent Proposal
Published 2026-03-24
Author(s) Lénárd Szolnoki
Audience
Revisions R0
Tracking issue View on GitHub
Abstract Being able to compare `meta::info` directly makes metaprogramming that needs to sort types, functions, etc... into some canonical order with standard algorithms more convenient.
Intent Proposal
Published 2026-03-30
Author(s) Aurelien Cassagnes
Audience
Tracking issue View on GitHub
Abstract The generative capability of reflection as they were introduced in C++26 are limited to `define_aggregate`, with no quick paths to more powerful facilities (See [p3294r2] for example). We can already leverage `define_aggregate` to impressive effects (See a JSON parser [here](https://brevzin.github.io/c++/2025/06/26/json-reflection/)), here we introduce another basic and lightweight building block:
Intent Informational
Published 2026-04-17
Author(s) Vinnie Falco
Audience
Tracking issue View on GitHub
Abstract C++ should make the safe thing easy, and the unsafe thing possible.
Intent Proposal
Published 2026-03-26
Author(s) Jan Schultke
Audience
Revisions R0
Tracking issue View on GitHub
Abstract Support for `unsigned char` and `signed char` in distributions would be useful. The ability to generate random bytes or octets is extremely valuable for [fuzz testing](https://en.wikipedia.org/wiki/Fuzzing). For example, when testing an implementation of an [LZ77 or LZ78](https://en.wikipedia.org/wiki/LZ77_and_LZ78) compression algorithm, a user would typically
Intent Proposal
Published 2026-03-10
Author(s) Jan Schultke
Audience
Tracking issue View on GitHub
Intent Proposal
Published 2026-04-01
Author(s) Jan Schultke
Audience
Tracking issue View on GitHub
Abstract The benefit of the range syntax is obvious: when there are several contiguous cases, it is much more concise than listing each case individually.
Intent Proposal
Published 2026-03-18
Author(s) Matthias Kretz
Audience
Tracking issue View on GitHub
Abstract | Document Number: | P4042R0 | | --- | --- | | Date: | 2026-03-18 | | Reply-to: | Matthias Kretz <m.kretz@gsi.de> | | Audience: | LWG | | Target: | C++26 |
Intent Proposal
Published 2026-03-07
Author(s) Darius Neațu
Audience , ,
Tracking issue View on GitHub
Abstract The C++ Contracts facility introduced by P2900 represents a major addition to the C++ language, intended to support specification of program correctness through preconditions, postconditions, and assertions.
Intent Proposal
Published 2026-03-08
Author(s) Lucian Radu Teodorescu
Audience
Tracking issue View on GitHub
Abstract C++26 contracts support a wide range of uses, but they currently cannot reliably enforce *UB-safety*. Because preconditions may be evaluated with *ignore* semantics, a library that relies on contract preconditions to prevent undefined behavior cannot guarantee that those checks will execute.
Intent Proposal
Published 2026-04-02
Author(s) Giuseppe D'Angelo
Audience , , , ,
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 Proposal
Published 2026-03-13
Author(s) Jan Schultke, Corentin Jabot
Audience
Tracking issue View on GitHub
Abstract Saturation arithmetic functions should be renamed. This paper resolves NB comment [[FR-026-265]](https://github%2ecom/cplusplus/nbballot/issues/840).
Intent Informational
Published 2026-04-17
Author(s) Vinnie Falco
Audience
Tracking issue View on GitHub
Abstract C++ already got an asynchronous model: regular C++20 coroutines.
Intent Informational
Published 2026-04-17
Author(s) Vinnie Falco
Audience
Tracking issue View on GitHub
Abstract The Environment parameter in `std::execution::task` makes cross-library coroutine interoperability structurally impossible without knowing every query by name.
Intent Informational
Published 2026-04-17
Author(s) Vinnie Falco
Audience
Tracking issue View on GitHub
Abstract The sender composition algebra does not apply to compound I/O results without losing data, and the construction that preserves all data produces code identical to the coroutine version.
Intent Informational
Published 2026-04-17
Author(s) Vinnie Falco
Audience
Tracking issue View on GitHub
Abstract Both coroutines and senders destroy compound data at an abstraction floor - the difference is that the sender floor sits below the composition algebra, and the coroutine floor is opt-in.
Intent Informational
Published 2026-04-17
Author(s) Vinnie Falco, Steve Gerbino
Audience
Tracking issue View on GitHub
Abstract A single class template bridges sender-based code into coroutine-native I/O with inline operation state, correct stop propagation, and automatic dispatch-back.
Intent Informational
Published 2026-04-17
Author(s) Vinnie Falco, Steve Gerbino
Audience
Tracking issue View on GitHub
Abstract Coroutine-native awaitables can be wrapped as senders, but compound I/O results must be reduced to an error code before crossing the bridge.
Intent Informational
Published 2026-04-17
Author(s) Vinnie Falco
Audience
Tracking issue View on GitHub
Abstract The unification of three working executor models had unanticipated downstream consequences.
Intent Informational
Published 2026-04-17
Author(s) Vinnie Falco
Audience
Tracking issue View on GitHub
Abstract Of the four deficiencies that [P1525R0](http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2019/p1525r0.pdf)[1] identified in `execute(F&&)`, three do not arise under the original framing of the callable as a continuation, and the fourth addresses a different question.
Intent Informational
Published 2026-04-17
Author(s) Vinnie Falco
Audience
Tracking issue View on GitHub
Abstract The committee set aside the Networking TS in 2021. The process had no mechanism to verify that the analysis examined every applicable framing, and no mechanism to revisit the outcome against evidence.
Intent Informational
Published 2026-04-17
Author(s) Vinnie Falco
Audience
Tracking issue View on GitHub
Abstract The committee expressed consensus that sender/receiver is a good basis for networking. The published evidence behind that word is documented here.
Intent Informational
Published 2026-04-17
Author(s) Vinnie Falco
Audience
Tracking issue View on GitHub
Abstract Published claims about executors, networking, and unification shaped a decade of committee decisions. The published evidence behind those claims is documented here.
Intent Informational
Published 2026-04-17
Author(s) Vinnie Falco
Audience
Tracking issue View on GitHub
Abstract Four decisions, each locally reasonable, each under-evidenced, produced a decade without networking in the C++ standard.
Intent Informational
Published 2026-04-17
Author(s) Vinnie Falco, Steve Gerbino, Michael Vandeberg, Mungo Gill, Mohammad Nejati
Audience
Tracking issue View on GitHub
Abstract C++ coroutines have five language mechanisms that combine into the ideal substrate for coroutine-native I/O.
Intent Proposal
Published 2026-03-24
Author(s) Barry Revzin, Peter Dimov, Daveed Vandevoorde, Dan Katz
Audience ,
Tracking issue View on GitHub
Abstract The Reflection design from [[P2996R13]](https://wg21.link/p2996r13) was based on a model of having consteval-only types to prevent reflections from leaking to runtime. But we’ve run into issues and limitations with that approach, so we propose that, for C++26, we change instead to a consteval-only value model. This solves the same problems, but has additional benefits.
Intent Proposal
Published 2026-04-02
Author(s) Giuseppe D'Angelo
Audience ,
Tracking issue View on GitHub
Abstract The sequence containers `vector`, `inplace_vector` and `deque` store their elements in contiguous storage (or, in the case of `deque`, in blocks of contiguous storage). When an element is erased from the middle of such a container, the elements after the erased position must be shifted to fill the gap. Similarly, when an element is inserted in the middle, the existing elements must be shifted to m
Intent Informational
Published 2026-04-17
Author(s) Mungo Gill
Audience
Tracking issue View on GitHub
Abstract A derivatives exchange is porting from Asio callbacks to coroutine-native I/O. Early results: it works.
Intent Informational
Published 2026-04-17
Author(s) Vinnie Falco, Klemens Morgenstern
Audience
Tracking issue View on GitHub
Abstract Senders pay a frame allocation to enter the awaitable protocol. They do not have to.
Intent Proposal
Published 2026-03-24
Author(s) Wyatt Childers
Audience ,
Tracking issue View on GitHub
Abstract If we take a step back and talk about types, a fundamental tenet is that types have invariants. These invariants are ultimately what drive many of the semantics of a C++ program. C++ would not be where it is today without RAII and RAII could not exist without a notion of invariants.
Intent Proposal
Published 2026-03-23
Author(s) Corentin Jabot
Audience
Revisions R0
Tracking issue View on GitHub
Abstract line-directive: # line pp-tokens new-line The string-literal of a #line directive, if present, shall be a character string literal. The line number of the current source line is the line number of the current physical source line, i.e., it is one greater than the number of new-line characters read or introduced in translation phase 1[lex.phases] while processing the source file to the current prep
Intent Informational
Published 2026-04-17
Author(s) Vinnie Falco
Audience
Tracking issue View on GitHub
Abstract The paper offers a way to measure what the type-safety profile actually covers.
Intent Proposal
Published 2026-04-20
Author(s) Vlad Serebrennikov
Audience ,
Revisions R1R0
Tracking issue View on GitHub
Abstract While looking at [CWG3103](https://cplusplus.github.io/CWG/issues/3103.html), I got interested how we arrived at status quo, specifically how [[basic.scope.scope]/3.1](https://wg21.link/basic.scope.scope#3.1) came to be, and this is what I found. One of the conclusions I arrived at is that it doesn’t make much sense to overload member functions with explicit object parameter of non-reference type
Intent Proposal
Published 2026-03-26
Author(s) Nathan Myers, Pablo Halpern
Audience
Revisions R0
Tracking issue View on GitHub
Abstract ``` Document #: P4139R1 Date: 2026-03-23 Project: ISO SC22/WG21 Programming Language C++ Title: Better better lookup Reply-to: ncm@cantrip.org Authors: Nathan Myers, Pablo Halpern Target: C++29 Audience: LEWG ```
Intent Proposal
Published 2026-03-23
Author(s) Gašper Ažman
Audience ,
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Intent Proposal
Published 2026-03-24
Author(s) Wyatt Childers
Audience
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Intent Proposal
Published 2026-03-27
Author(s) S. Davis Herring
Audience
Tracking issue View on GitHub
Abstract This paper partially addresses US 33 (065) by clarifying what evaluations of a (putative) constant expression take place. It does not proceed further as would be necessary to support visible side effects during translation (*e.g.*, output as in [P2758](https://www.open-std.org/JTC1/SC22/WG21/docs/papers/2025/p2758r5.html)) because those do not exist in C++26.
Intent Proposal
Published 2026-03-26
Author(s) Mark Hoemmen, Tomasz Kamiński, Tim Song, Jonathan Wakely
Audience
Revisions R0
Tracking issue View on GitHub
Abstract This paper expresses [LWG4520](https://cplusplus.github.io/LWG/issue4520) and proposes fixing it by reverting adoption of [P2447R6](https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2023/p2447r6.html).
Intent Proposal
Published 2026-03-25
Author(s) Jonathan Wakely
Audience
Tracking issue View on GitHub
Intent Proposal
Published 2026-03-27
Author(s) Jonathan Wakely
Audience
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Intent Proposal
Published 2026-04-20
Author(s) Jonathan B. Coe, Hana Dusikova, Antony Peacock, Philip Craig, Neelofer Banglawala
Audience ,
Tracking issue View on GitHub
Abstract We propose `protocol<T,` `A>` and `protocol_view<T>`, standard library vocabulary types for structural subtyping in C++. Interfaces are specified as plain structs; any type whose member functions satisfy the interface is accepted without requiring explicit inheritance.
Intent Proposal
Published 2026-03-27
Author(s) Andrzej Krzemieński, Brian Bi
Audience ,
Revisions R0
Tracking issue View on GitHub
Intent Proposal
Published 2026-04-16
Author(s) Nicolas Morales, Mark Hoemmen, Bryce Adelstein Lelbach, Damien Lebrun-Grandie
Audience
Tracking issue View on GitHub
Abstract | **Before** | **After** | | --- | --- | | `std::ranges::for_each( std::execution::par_unseq, std::views::cartesian_product( std::views::indices(A.extent(0)), std::views::indices(A.extent(1))), [=] (auto idx) { auto [i, j] = idx; B[j, i] = A[i, j]; });` | `std::for_each_index( std::execution::par_unseq, A.mapping(), [=] (auto i, auto j) { B[j, i] = A[i, j]; });` |
Intent Proposal
Published 2026-03-27
Author(s) Robert Leahy
Audience
Revisions R0
Tracking issue View on GitHub
Abstract When `std::execution::affine_on` was added [1] it was a binary-invocable object accepting two parameters, respectively:
Intent Proposal
Published 2026-03-27
Author(s) Tim Song, Ruslan Arutyunyan, Arthur O’Dwyer
Audience
Tracking issue View on GitHub
Abstract This paper provides replacement wording for the following papers:
Intent Proposal
Published 2026-03-26
Author(s) Oliver Hunt
Audience
Tracking issue View on GitHub
Abstract P3937 presents a discussion of the type erasure requirements for any future trivial relocation feature in C++. This paper is a very short response to that paper addressing various issue in the presented requirements, and erroneous technical arguments.
Intent Proposal
Published 2026-03-27
Author(s) Ville Voutilainen
Audience
Tracking issue View on GitHub
Abstract This paper proposes wording to resolve the NB comment [FR-017-155](https://github.com/cplusplus/nbballot/issues/734).
Intent Proposal
Published 2026-03-26
Author(s) Jan Schultke
Audience
Tracking issue View on GitHub
Abstract C23 now has `_BitInt` type for N-bit integers (WG14 N2763, N2775):
Intent Proposal
Published 2026-03-27
Author(s) Oliver Hunt
Audience
Tracking issue View on GitHub
Intent Proposal
Published 2026-03-27
Author(s) Tim Song
Audience
Tracking issue View on GitHub
Abstract In response to LEWG direction on [LWG4361], this paper provides wording to make the `receiver_of` and `sender_to` concepts exposition-only for C++26.
Intent Proposal
Published 2026-03-27
Author(s) Jens Maurer
Audience
Tracking issue View on GitHub
Intent Proposal
Published 2026-04-01
Author(s) Jeff Snyder, Jonathan B. Coe, Neelofer Banglawala
Audience ,
Tracking issue View on GitHub
Intent Proposal
Published 2026-04-05
Author(s) Jan Schultke
Audience
Tracking issue View on GitHub
Abstract This paper supersedes [[P2827R1]](https://wg21%2elink/p2827r1) and fixes [[LWG3081]](https://wg21%2elink/LWG3081), [[LWG3082]](https://wg21%2elink/LWG3082), and [[LWG3456]](https://wg21%2elink/LWG3456). It is intended as a defect report for C++17. The handling of floating-point overflow and underflow in `std::from_chars` is inconsistent; the implementations diverge from each other, and every imple
Intent Informational
Published 2026-04-17
Author(s) Vinnie Falco, Steve Gerbino
Audience
Tracking issue View on GitHub
Abstract This paper documents the design rationale for the *IoAwaitable* protocol.
Intent Proposal
Published 2026-04-15
Author(s) Hewill Kang
Audience ,
Tracking issue View on GitHub
Abstract Standard `mdspan` accessors, such as `default_accessor`, are specialized for use with raw pointers. While `mdspan`'s design allows for custom accessors, providing a standardized iterator-based accessor simplifies integration with ranges such as views and containers.
Intent Proposal
Published 2026-04-02
Author(s) Emanuel Spiridon
Audience
Tracking issue View on GitHub
Abstract This paper explores the possibility of adding a library addition to <type_traits> to assist the programmer when writing concept constraints. Concept constraints can be written by using the std::is_same_v tool, however the compile time logic is hard to understand, and at times, are error-prone at scale. An issue that modern concept constraints have is that, despite how simple it is once you impleme
Intent Proposal
Published 2026-04-04
Author(s) Matheus Izvekov
Audience ,
Tracking issue View on GitHub
Abstract This paper proposes to relax some Class Template Argument deduction (CTAD) restrictions which were originally put in place for no well motivated reason other than simplicity and being conservative.
Intent Proposal
Published 2026-04-20
Author(s) Vlad Serebrennikov
Audience
Tracking issue View on GitHub
Abstract 7.6.1 [[expr.post]](https://wg21.link/expr.post) lists all the grammar at the top, while the rest of the subclause resorts to either quoting the grammar or describing it with words. This paper aims to improve the situation, introducing new nonterminals and putting their definitions in the respective subclauses.
Intent Proposal
Published 2026-04-20
Author(s) Hewill Kang
Audience , ,
Tracking issue View on GitHub
Abstract This paper provides `rbegin()`/`rend()`/`crbegin()`/`crend()` methods to `ranges::view_interface`, making its interface more symmetric with the existing `cbegin()`/`cend()` members and enhancing convenience for views. Revision history R0 Initial revision. Discussion In C++23, `view_interface` added `cbegin()`/`cend()` members to improve const-correctness and interface consistency. However, it stil
Intent Informational
Published 2026-04-17
Author(s) Mungo Gill
Audience
Tracking issue View on GitHub
Abstract Every mailing repeats the same deployment background. This paper puts one citeable inventory in the record.
Intent Proposal
Published 2026-04-13
Author(s) Peter Bindels
Audience
Tracking issue View on GitHub
Abstract This paper proposes a tentative plan for making progress on safety and profiles in C++. If adopted, this plan could allow SG23, EWG, and CWG to finalise the design and wording for profiles in time for inclusion of this feature in C++29.
Intent Proposal
Published 2026-03-30
Author(s) Stephane Gros-Lemesre
Audience , , ,
Tracking issue View on GitHub
Intent Proposal
Published 2026-04-16
Author(s) Mark Hoemmen, Hana Dusíková, Rob Parolin
Audience
Tracking issue View on GitHub
Abstract [P4144R1](https://isocpp.org/files/papers/P4144R1.html) reverted [P2447R6](https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2023/p2447r6.html) by removing `span`’s `initializer_list` constructor. We propose to add it back in C++29, but with constraints this time, in order to avoid the unfortunate conversions that led to its removal.
Intent Proposal
Published 2026-04-17
Author(s) Robert Leahy
Audience ,
Tracking issue View on GitHub
Abstract Under the original design of `std::execution` [1] one could check whether or not `std::execution::connect` threw an exception via:
Intent Proposal
Published 2026-04-20
Author(s) Vlad Serebrennikov
Audience
Tracking issue View on GitHub
Abstract There are multiple open Core issues against 6.8.3 [[basic.align]](https://wg21.link/basic.align) ([1211](https://cplusplus.github.io/CWG/issues/1211.html), [2840](https://cplusplus.github.io/CWG/issues/2840.html)) and 9.13.2 [[dcl.align]](https://wg21.link/dcl.align) ([1617](https://cplusplus.github.io/CWG/issues/1617.html), [2223](https://cplusplus.github.io/CWG/issues/2223.html), [3024](https://
Intent Proposal
Published 2026-04-19
Author(s) Giuseppe D'Angelo
Audience ,
Tracking issue View on GitHub
Abstract Trivial relocation has been a long-standing goal for C++. Multiple proposals have been put forward over the years, most notably [P1144R12] and [P2786R13], each with a different design and different tradeoffs. In the C++26 cycle, [P2786R13] was adopted in Hagenberg, but was ultimately removed from the C++26 Working Draft in Kona due to a number of unresolved design concerns.
· source: open-std.org