WG21 MAILINGS

Mailings

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

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May 2026 Papers

⧉ open-std.org

116 papers · WG21 mailing

A WG21 mailing is the month's batch of papers under committee review.
Intent Informational
Published 2026-05-12
Author(s) Hana Dusíková
Audience
Abstract [WG21](mailto:WG21 (YOU-NEED-JAVASCRIPT-ENABLED) #V0cyMSA8YWxsQGxpc3RzLmlzb2NwcC5vcmc+P3N1YmplY3Q9TjUwNDQ6IEJybm8gSnVuZSAyMDI2IFZlbnVlICgybmQgcmV2aXNpb24p)
Intent Informational
Published 2026-04-29
Author(s) Nina Ranns
Audience
Abstract | Doc. No.: | N5045 | | --- | --- | | Date: | 2026-04-29 | | Reply to: | [Nina Dinka Ranns](mailto:dinka.ranns@gmail.com) |
Intent Informational
Author(s) Thomas Köppe
Audience
Intent Informational
Published 2026-05-12
Author(s) Thomas Köppe
Audience
Intent Proposal
Published 2026-05-11
Author(s) Oliver Kowalke, Nat Goodspeed
Audience ,
Revisions R22
Tracking issue View on GitHub
Abstract This paper proposes a minimal API that enables stackful context switching **without** the need for a scheduler. The API is suitable to act as building-block for high-level constructs such as stackful coroutines as well as cooperative multitasking (aka user-land/green threads that incorporate a **scheduling** facility).
Intent Proposal
Published 2026-05-12
Author(s) JeanHeyd Meneide
Audience , ,
Revisions R9
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 Informational
Published 2026-05-01
Author(s) Mungo Gill, Vinnie Falco
Audience
Revisions R3R2R1R0
Tracking issue View on GitHub
Abstract C++20 provides symmetric transfer ([P0913R1](https://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 2026-05-12
Author(s) Eddie Nolan
Audience , ,
Revisions R11
Tracking issue View on GitHub
Intent Proposal
Published 2026-05-12
Author(s) Gašper Ažman
Audience
Tracking issue View on GitHub
Abstract This paper introduces a way to rewrite a function call to a different expression without a forwarding layer.
Intent Proposal
Published 2026-05-10
Author(s) Bernhard Manfred Gruber, Yihan Wang, Mark Hoemmen
Audience
Tracking issue View on GitHub
Abstract [[P0009R18]](https://wg21.link/p0009r18) proposed `std::mdspan` , which was approved for C++23. It comes with the utility class template `std::extents` to describe the integral extents of a multidimensional index space. Practically, `std::extents` models an array of integrals, where some of the values can be specified at compile-time. However, `std::extents` behaves very little like an array. A no
Intent Proposal
Published 2026-05-12
Author(s) Daniel Towner, Ruslan Arutyunyan
Audience
Revisions R3R2
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, or cal
Intent Proposal
Published 2026-05-12
Author(s) Daniel Towner, Ruslan Arutyunyan
Audience ,
Revisions R3R2
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 of *built-in vectorizable* types: arithmetic types and `std::complex` specializations. This paper proposes a minimal change to the specification in which this list is extended. Firstly, `std::byte` is added to the closed list as a standard library type with fixed seman
Intent Proposal
Published 2026-05-12
Author(s) Mateusz Pusz, Dominik Berner, Johel Ernesto Guerrero Peña, Charles Hogg, Nicolas Holthaus, Roth Michaels, Vincent Reverdy
Audience , , ,
Revisions R7
Tracking issue View on GitHub
Abstract Several groups in the ISO C++ Committee reviewed the “P1935: A C++ Approach to Physical Units” [[P1935R2]](https://wg21.link/p1935r2) proposal in Belfast 2019 and Prague 2020. All those groups expressed interest in the potential standardization of such a library and encouraged further work. The authors also got valuable initial feedback that highly influenced the design of the V2 version of the [[
Intent Proposal
Published 2026-05-11
Author(s) Timur Doumler, Joshua Berne
Audience
Tracking issue View on GitHub
Abstract We propose to allow specifying precondition and postcondition assertions on virtual functions, in the same way they can already be specified on non-virtual functions:
Intent Proposal
Published 2026-05-12
Author(s) Timur Doumler, Gašper Ažman, Joshua Berne
Audience , ,
Tracking issue View on GitHub
Abstract We propose to add a new, optional syntactic construct to postcondition assertions, called *postcondition* captures. Postcondition captures are spelled in the same fashion as lambda captures. They are placed immediately after the `post` contextual keyword and before the predicate: `post [``captures``] (``predicate``)` Postcondition captures are variables constructed when the function is called. The
Intent Proposal
Published 2026-05-11
Author(s) Timur Doumler, Peter Bindels, Joshua Berne
Audience
Tracking issue View on GitHub
Abstract A user-defined diagnostic message can provide additional information that can help developers more quickly understand why a particular assertion failed and how to resolve the issue. The ability to optionally provide such a message is valuable for any assertion facility, including contract assertions. The C `assert` macro does not directly support an associated diagnostic message. However, the idio
Intent Proposal
Published 2026-05-12
Author(s) Timur Doumler, Joshua Berne
Audience ,
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.
Intent Proposal
Published 2026-05-10
Author(s) Jan Schultke
Audience
Tracking issue View on GitHub
Abstract The C++ bit manipulation library in `<bit>` is an invaluable abstraction from hardware operations. Functions like `countl_zero` help the programmer avoid use of intrinsic functions or inline assembly.
Intent Proposal
Published 2026-05-12
Author(s) Hana Dusíková
Audience ,
Tracking issue View on GitHub
Abstract Pointer tagging is widely known and used technique ([Glasgow Haskell Compiler](https://takenobu-hs.github.io/downloads/haskell_ghc_illustrated.pdf), LLVM's `[PointerIntPair](https://github.com/llvm/llvm-project/blob/8e5aa538caccef167e8096b2173fdaf2be9cc129/llvm/include/llvm/ADT/PointerIntPair.h#L80)`, `[PointerUnion](https://github.com/llvm/llvm-project/blob/8e5aa538caccef167e8096b2173fdaf2be9cc12
Intent Proposal
Published 2026-05-02
Author(s) Joshua Berne, Timur Doumler, John Lakos
Audience
Tracking issue View on GitHub
Abstract **–** Specified use of `source_location::current()` and discussed implementation choices
Intent Proposal
Published 2026-04-27
Author(s) Yihe Li
Audience
Tracking issue View on GitHub
Abstract The motivation for this view is given in [P2760R1] and quoted below for convenience:
Intent Proposal
Published 2026-05-12
Author(s) Hana Dusíková, Gašper Ažman
Audience ,
Tracking issue View on GitHub
Abstract | functionality | runtime only (current status) | runtime & constexpr compatible replacement | status | | --- | --- | --- | --- | | pointer ↔︎ integer | `intptr_t * iptr = reinterpret_cast<intptr_t>(ptr); auto * optr = reinterpret_cast<pointer>(iptr);` | — | not proposed | | pointer tagging | `auto tptr = reinterpret_cast<pointer>( reinterpret_cast<intptr_t>(ptr) \| 0b1u); auto tag = static_cast<b
Intent Proposal
Published 2026-05-11
Author(s) Joshua Berne
Audience
Tracking issue View on GitHub
Abstract — Major restructuring: new Introduction, Design, Glossary, expanded Standard Library Additions sections
Intent Proposal
Published 2026-05-09
Author(s) Hui Xie, S. Levent Yilmaz, Louis Dionne, Patrick Roberts
Audience ,
Revisions R5
Tracking issue View on GitHub
Abstract This paper proposes a new type-erased view: `std::ranges::any_view`. That type-erased view allows customizing the traversal category of the view, its value type and a few other properties. For example:
Intent Proposal
Published 2026-05-11
Author(s) Maged Michael, Michael Wong, Paul McKenney, Mark de Wever
Audience
Revisions R3
Tracking issue View on GitHub
Abstract This paper proposes extending the C++26 hazard pointer interface to support synchronous reclamation. This revision, P3427R4, revises R3 by following LEWG Croydon 2026 feedback.
Intent Proposal
Published 2026-05-11
Author(s) Maged Michael, Michael Wong, Paul McKenney
Audience
Tracking issue View on GitHub
Abstract This paper proposes extending the C++26 hazard pointer interface to support creation and destruction of batches of nonempty hazard pointers. This revision P3428R3 revises R2 by following LEWG Croydon 2026 feedback. It is ready for review by LWG in Brno 2026.
Intent Proposal
Published 2026-05-10
Author(s) Jan Schultke
Audience ,
Tracking issue View on GitHub
Abstract While C++ already has a broad selection of control flow constructs, one construct commonly found in other languages is notably absent: the ability to apply `break` or `continue` to a loop or `switch` when this isn’t the innermost enclosing statement. This feature is popular, simple, and quite useful:
Intent Proposal
Published 2026-05-11
Author(s) Joshua Berne, Timur Doumler, Jens Maurer, Shafik Yaghmour
Audience
Revisions R1R0
Tracking issue View on GitHub
Intent Proposal
Published 2026-05-10
Author(s) Jan Schultke
Audience
Revisions R4
Tracking issue View on GitHub
Abstract [Carry-less multiplication](https://en.wikipedia.org/wiki/Carry-less_product) is a simple numerical operation on unsigned integers. It can be a seen as a regular multiplication where `xor` is being used as a reduction instead of `+`.
Intent Proposal
Published 2026-05-12
Author(s) Jan Schultke
Audience ,
Revisions R3
Tracking issue View on GitHub
Abstract In distant history, there have been various attempts at standardizing multi-precision integers in C++, such as [[N1692]](https://wg21%2elink/n1692) "A Proposal to add the Infinite Precision Integer to the C++ Standard Library", [[N1744]](https://wg21%2elink/n1744) "Big Integer Library Proposal for C++0x", and [[N4038]](https://wg21%2elink/n4038) "Proposal for Unbounded-Precision Integer Types", al
Intent Proposal
Published 2026-05-10
Author(s) Matthew Taylor, Alex (Waffl3x)
Audience
Tracking issue View on GitHub
Abstract Postfix increment and decrement operators have a default behaviour which already exists in the mind of every C++ developer - make a copy, increment/decrement the original, and return the copy. The canonical implementation of this default can always be expressed entirely in terms of other operations (prefix increment/decrement and copy-construction), in a manner which is entirely agnostic to any ot
Intent Proposal
Published 2026-05-10
Author(s) Jan Schultke
Audience
Revisions R3
Tracking issue View on GitHub
Abstract C++ currently only offers truncating integer division in the form of the `/` operator. However, other rounding modes have various use cases too, and implementing these as the user can be surprisingly hard, especially when integer overflow needs to be avoided, and negative inputs are accepted.
Intent Proposal
Published 2026-05-06
Author(s) Michael Florian Hava
Audience
Tracking issue View on GitHub
Abstract ```cpp template<typename T, size_type E = dynamic_extent> struct span { … //runtime subsetting: constexpr span subspan(size_type pos = 0, size_type n = dynamic_extent) const; constexpr span first(size_type count) const; constexpr span last(size_type count) const; … }; template<typename charT, typename traits = char_traits<charT>> struct basic_string_view { … //in place shrinking: constexpr void re
Intent Proposal
Published 2026-05-11
Author(s) Jan Schultke
Audience
Revisions R3
Tracking issue View on GitHub
Abstract The `std::array` class template has established itself as a de-facto replacement for "builtin arrays" or "C-style arrays" in many code bases. This also means that it is frequently taught to novice programmers, with an explanation along the lines of:
Intent Proposal
Published 2026-05-06
Author(s) Yihan Wang
Audience
Tracking issue View on GitHub
Abstract This paper introduce constraints for `std::make_from_tuple` to make it SFINAE friendly.
Intent Proposal
Published 2026-05-12
Author(s) Matt Cummins, Valentyn Yukhymenko
Audience
Revisions R2
Tracking issue View on GitHub
Abstract This paper proposes a new standard library template, `consteval_hash<T>`, with a single specialization for `meta::info`. The purpose of this facility is to provide a standard interface for compile-time hashing, thereby allowing unordered containers such as `unordered_map` and `unordered_set` to be used with `meta::info` keys, and potentially with other types in future.
Intent Proposal
Published 2026-05-12
Author(s) Hana Dusíková
Audience ,
Tracking issue View on GitHub
Abstract To make `constexpr` exception support complete, and allow all functionality withing constant evaluation. This paper was seen in previous revision by LEWG. It didn't get consensus and most of the group prefered the conservative approach of removing `constexpr` from `std::uncaught_exception()` and `std::current_exception()`. The group asked me to revisit this again for C++29.
Intent Proposal
Published 2026-05-12
Author(s) Timur Doumler, Joshua Berne
Audience ,
Tracking issue View on GitHub
Intent Proposal
Published 2026-05-12
Author(s) Hana Dusíková
Audience
Tracking issue View on GitHub
Abstract At first maybe this does seem as somehow arcane or esoteric. But this is a problem worth solving and it will make C++ a bit more expressive.
Intent Proposal
Published 2026-05-11
Author(s) Jan Schultke, Peter Bindels
Audience
Revisions R1
Tracking issue View on GitHub
Abstract Support for `char8_t` and other Unicode character types in `std::to_chars` and `std::from_chars` is clearly useful. File formats such as JSON require the use of Unicode character encodings, so an application that deals with JSON may want to use `char8_t` in its APIs and internally. However, when attempting to use `char8_t` for this purpose, one quickly runs into problems:
Intent Proposal
Published 2026-05-11
Author(s) Jan Schultke
Audience ,
Tracking issue View on GitHub
Abstract The current C++ syntax notation as specified in [[syntax]](https://eel.is/c++draft/syntax) and summarized in [[gram]](https://eel.is/c++draft/gram) has only a handful of features:
Intent Proposal
Published 2026-05-12
Author(s) Hana Dusíková, NylteJ
Audience
Tracking issue View on GitHub
Abstract C++ users are often surprised by missing functionality available during constant evaluation, sometimes there is no real reason in the language, it's just no one wrote a paper making the thing `constexpr`. Anecdotally this is often surprise to Jason Turner's students when they start experimenting with `constexpr` code.
Intent Proposal
Published 2026-05-11
Author(s) Jan Schultke
Audience
Tracking issue View on GitHub
Abstract [[P3348R4]](https://wg21%2elink/p3348r4) rebased the C++26 standard on C23; it previously referred to C17. However, this process was deliberately left incomplete: some of the new C23 `<math.h>` features are only used by decimal floating-point types, or they require core language changes, etc.
Intent Proposal
Published 2026-05-11
Author(s) Jan Schultke
Audience ,
Revisions R0
Tracking issue View on GitHub
Abstract The following use of `std::bit_cast` has undefined behavior at compile time:
Intent Proposal
Published 2026-04-30
Author(s) Daniel Towner
Audience
Revisions R0
Tracking issue View on GitHub
Abstract Modern C++ provides powerful facilities for generic programming, but lacks a uniform way to change the element type of containers and container-like types. Consider a simple requirement: convert a container of `float` into the corresponding container of `double`, without the caller having to know what kind of container it is.
Intent Proposal
Published 2026-05-12
Author(s) Daniel Towner
Audience
Revisions R0
Tracking issue View on GitHub
Abstract SIMD programming frequently requires reinterpreting vector data at different element granularities—converting packed bytes to shorts, accessing the bit representation of floats, or regrouping data for different operations. While platform intrinsics have long supported this pattern naturally, with `std::simd` programmers must use `std::bit_cast` with fully-specified target types, manually computing
Intent Proposal
Published 2026-05-12
Author(s) Daniel Towner, Ruslan Arutyunyan
Audience , ,
Revisions R1R0
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 similarly unspecified.
Intent Proposal
Published 2026-05-01
Author(s) Vinnie Falco, Mungo Gill, Steve Gerbino
Audience
Revisions R2R1R0
Tracking issue View on GitHub
Abstract This paper asks the committee to advance the *IoAwaitable* protocol as a standard coroutine execution model.
Intent Informational
Published 2026-05-01
Author(s) Vinnie Falco, Mungo Gill
Audience
Revisions R2R1R0
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 C
Intent Proposal
Published 2026-05-12
Author(s) Hana Dusíková
Audience
Tracking issue View on GitHub
Abstract Often you just need to pass a value around, but not interact with it, for that in C++ you have multiple options: template (and keep the type information intact), inheritance (and being force to use intrusive inheritance in your types), passing allocated `(const) void *` pointer (and managing its lifetime), alternatively use `std::unique_ptr` or `std::shared_ptr` with custom deleters, or use a poly
Intent Informational
Published 2026-05-01
Author(s) Vinnie Falco, Mungo Gill
Audience
Revisions R1R0
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 2026-05-10
Author(s) Michael Wong, phil Ratzloff
Audience
Revisions R1R0
Tracking issue View on GitHub
Intent Informational
Published 2026-05-01
Author(s) Vinnie Falco
Audience
Revisions R0
Tracking issue View on GitHub
Abstract C++ should make the safe thing easy, and the unsafe thing possible.
Intent Informational
Published 2026-05-01
Author(s) Vinnie Falco
Audience
Tracking issue View on GitHub
Abstract C++ has bytes. A contiguous region of bytes needs a type. A sequence of such regions needs another. This paper examines the types that predictably come to mind, and their consequences.
Intent Informational
Published 2026-05-01
Author(s) Vinnie Falco
Audience
Tracking issue View on GitHub
Abstract C++20 standardized coroutines. C++26 adds `std::execution`. Both are asynchronous models. The question is whether the
Intent Informational
Published 2026-05-01
Author(s) Vinnie Falco
Audience
Tracking issue View on GitHub
Abstract We interviewed five experts, had AI distill their wisdom into 11 principles, built a scoring rubric, and graded our own paper first.
Intent Informational
Published 2026-05-01
Author(s) Vinnie Falco
Audience
Tracking issue View on GitHub
Abstract This paper collects dated, public, falsifiable predictions about `std::execution` from proponents and critics alike, and checks each against the record.
Intent Informational
Published 2026-05-01
Author(s) Vinnie Falco
Audience
Tracking issue View on GitHub
Intent Informational
Published 2026-05-01
Author(s) Vinnie Falco
Audience
Revisions R0
Tracking issue View on GitHub
Abstract C++ already got an asynchronous model: regular C++20 coroutines.
Intent Informational
Published 2026-05-01
Author(s) Vinnie Falco
Audience
Revisions R0
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 2026-05-01
Author(s) Vinnie Falco
Audience
Revisions R0
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 2026-05-01
Author(s) Vinnie Falco
Audience
Revisions R0
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 2026-05-01
Author(s) Vinnie Falco, Steve Gerbino
Audience
Revisions R0
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 2026-05-01
Author(s) Vinnie Falco, Steve Gerbino
Audience
Revisions R0
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 2026-05-01
Author(s) Vinnie Falco
Audience
Revisions R0
Tracking issue View on GitHub
Abstract The unification of three working executor models had unanticipated downstream consequences.
Intent Informational
Published 2026-05-01
Author(s) Vinnie Falco
Audience
Revisions R0
Tracking issue View on GitHub
Abstract Of the four deficiencies that [P1525R0](https://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 2026-05-01
Author(s) Vinnie Falco
Audience
Revisions R0
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 2026-05-01
Author(s) Vinnie Falco
Audience
Revisions R0
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 2026-05-01
Author(s) Vinnie Falco
Audience
Revisions R0
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 2026-05-01
Author(s) Vinnie Falco
Audience
Revisions R0
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 2026-05-01
Author(s) Vinnie Falco, Steve Gerbino, Michael Vandeberg, Mungo Gill, Mohammad Nejati
Audience
Revisions R0
Tracking issue View on GitHub
Abstract C++ coroutines have five language mechanisms that combine into the ideal substrate for coroutine-native I/O.
Intent Informational
Published 2026-05-01
Author(s) Vinnie Falco
Audience
Tracking issue View on GitHub
Abstract Every concession granted. The gap remains. I/O users pay for what they do not need.
Intent Informational
Published 2026-05-01
Author(s) Vinnie Falco
Audience
Tracking issue View on GitHub
Abstract `std::execution::when_all` dispatches on channels. I/O errors arrive on the value channel. The combinator does not see them.
Intent Informational
Published 2026-05-19
Author(s) Mungo Gill
Audience
Revisions R0
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 2026-05-01
Author(s) Vinnie Falco, Klemens Morgenstern
Audience
Revisions R0
Tracking issue View on GitHub
Abstract Senders pay a frame allocation to enter the awaitable protocol. They do not have to.
Intent Informational
Published 2026-05-01
Author(s) Vinnie Falco
Audience
Tracking issue View on GitHub
Abstract The coroutine frame allocator must arrive before the coroutine frame exists. Exactly two mechanisms can deliver it.
Intent Proposal
Published 2026-03-24
Author(s) Corentin Jabot
Audience
Revisions R1R0
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 Proposal
Published 2026-05-08
Author(s) Nathan Myers, Pablo Halpern
Audience
Revisions R1R0
Tracking issue View on GitHub
Abstract [[P3091R5]](https://wg21.link/p3091r5), forwarded to LWG for C++29, adds member functions `get` to associative containers in the Standard Library. These member functions work like `operator[]` or `at`, but return an `optional<T&>` value instead of a simple reference; when lookup fails, they return the empty object. While the feature was strongly favored, support for the name `get` yielded only a w
Intent Proposal
Published 2026-05-12
Author(s) Hana Dusíková
Audience
Tracking issue View on GitHub
Abstract This paper introduces a customization point which is called when a constant-evaluated value is moving outside of its constant-evaluation (like initialization of `constexpr` variable, or `consteval` function emitting a value to an expression / function evaluated at runtime).
Intent Proposal
Published 2026-05-12
Author(s) Jonathan B. Coe, Hana Dusikova, Antony Peacock, Philip Craig, Neelofer Banglawala
Audience
Revisions R0
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 Informational
Published 2026-05-01
Author(s) Vinnie Falco
Audience
Tracking issue View on GitHub
Abstract Frame-visible coroutines would eliminate `std::execution::task`'s heap allocation and give sender-based coroutine algorithms full optimizer visibility.
Intent Proposal
Published 2026-05-12
Author(s) Hana Dusíková
Audience
Tracking issue View on GitHub
Abstract This papers provides a customization for ADL via a annotation to add an entity to be associated with a type. It adds a new `<meta>` type to represent the annotation, and it modifies [`[basic.lookup.argdep]`](https://eel.is/c++draft/basic.lookup.argdep)
Intent Informational
Published 2026-05-31
Author(s) Vinnie Falco
Audience
Tracking issue View on GitHub
Abstract Thirty-four papers audit two decades of async decisions, deploy coroutine-native I/O at a derivatives exchange with zero per-operation allocations, bridge the result to std::execution, and deliver open-source AI evaluation tools for WG21 proposals.
Intent Informational
Published 2026-05-01
Author(s) Vinnie Falco, Steve Gerbino
Audience
Revisions R0
Tracking issue View on GitHub
Abstract This paper documents the design rationale for the *IoAwaitable* protocol.
Intent Proposal
Published 2026-05-12
Author(s) Vlad Serebrennikov
Audience
Revisions R0
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 non-terminals and putting their definitions in the respective subclauses.
Intent Informational
Published 2026-05-01
Author(s) Vinnie Falco
Audience
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Abstract Sections of P2300R10 are compared to other sections of P2300R10 and entered into the historical record.
Intent Informational
Published 2026-05-01
Author(s) Mungo Gill
Audience ,
Revisions R0
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Abstract Every mailing repeats the same deployment background. This paper puts one citeable inventory in the record.
Intent Proposal
Published 2026-05-11
Author(s) Mateusz Pusz
Audience
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Abstract [[P3045R7]](https://wg21.link/p3045r7) proposes a C++ quantities and units framework built on two core abstractions: `quantity` (displacement vectors) and `quantity_point` (points in an affine space). Real-world experience with the **[[mp-units]](https://mpusz.github.io/mp-units)** reference implementation, together with feedback from SG6, BSI, ANSI, and the broader C++ community, shows that this
Intent Proposal
Published 2026-05-12
Author(s) Nevin Liber
Audience
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Abstract There is no easy, obvious way to retrieve the pointer stored in an `optional<T&>` , nor a pointer to the object in an `optional<T>` This proposal rectifies that by proposing a `.get_ptr()` method.
Intent Proposal
Published 2026-04-17
Author(s) Abdul Muneem
Audience
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Intent Proposal
Published 2026-04-29
Author(s) Yihe Li
Audience
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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.
Intent Proposal
Published 2026-04-30
Author(s) Barry Revzin, Zach Laine, Matthias Kretz, Jonathan Wakely, Tomasz Kamiński
Audience
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Abstract Originally, the design of `std::constant_wrapper` [[P2781R4]](https://wg21.link/p2781r4) was :
Intent Informational
Published 2026-05-01
Author(s) Vinnie Falco
Audience
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Abstract For less than a dollar, every paper in the mailing can know its own weaknesses before the committee does.
Intent Informational
Published 2026-05-01
Author(s) Vinnie Falco
Audience
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Abstract An AI examines [P2900R14](https://wg21.link/p2900r14) "Contracts for C++" by applying the Advocatus Diaboli from [P4207R0](https://isocpp.org/files/papers/P4207R0.pdf) "Prosecute Your Paper To
Intent Proposal
Published 2026-04-28
Author(s) Daniel Towner
Audience ,
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Abstract The SIMD working draft introduces `std::simd::basic_vec<T, Abi>` as an element-wise parallel extension of an element type `T`. A central goal is to allow the same generic numeric code to operate on scalar `T` and on `basic_vec<T, Abi>` interchangeably. Most non-trivial numeric code that aims for that behaviour would require `std::numeric_limits<V>` somewhere. For example:
Intent Proposal
Published 2026-05-05
Author(s) Daniel Pfeifer
Audience
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Abstract We propose the addition of a new class template `copy_on_write<T>` to the C++ Standard Library.
Intent Proposal
Published 2026-05-05
Author(s) Yihe Li
Audience
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Abstract This proposal introduces a family of adaptors that convert closed ranges into half-open ranges, as expected by most other standard library facilities in C++, thus providing direct support for a range model that has been fundamentally incompatible with the C++ iterator model until now.
Intent Proposal
Published 2026-05-11
Author(s) Guy Davidson
Audience
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Abstract This proposal introduces a new Annex specifying ISO/IEC 60559 conformance. There are nine clauses that need to be considered from ISO/IEC 60559:2020, clauses 3 to 11. [559] offers binary and decimal floating-point arithmetic features. This proposal will only introduce binary floating-point feature support.
Intent Proposal
Published 2026-05-08
Author(s) Mateusz Pusz
Audience
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Abstract [[P3045R8]](https://wg21.link/p3045r8) supplies the type system. It does not supply the SI. A user who includes the framework gets `quantity` , `unit` , `quantity_spec` , `prefix` — but no `metre` , no `kilogram` , no `second` . The framework is deliberately content-agnostic: it supports arbitrary systems of quantities and units. Shipping the framework without SI content would be like shipping `<a
Intent Proposal
Published 2026-05-10
Author(s) Lucian Radu Teodorescu
Audience
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Abstract Correctness is usually harder to discuss than the individual properties from which it is built. Following Lamport’s division of correctness into safety and liveness [[Lamport77]](https://lamport.azurewebsites.net/pubs/proving.pdf), this paper argues that C++ standardization should treat progress guarantees as part of the correctness contract of concurrency facilities.
Intent Proposal
Published 2026-05-12
Author(s) Lucian Radu Teodorescu
Audience
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Abstract C++26 senders provide a vocabulary for composing asynchronous work, but they do not by themselves provide sender-native equivalents of synchronization primitives that impose non-local concurrency constraints. Programs still need to serialize unrelated operations, bound concurrency across independently submitted work, wait for readiness, and coordinate completion or phase boundaries.
Intent Proposal
Published 2026-05-07
Author(s) Michael Florian Hava
Audience
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Intent Proposal
Published 2026-05-06
Author(s) Robert Leahy
Audience ,
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Abstract The standard currently specifies, by fiat, that `std::execution::when_all()` is ill-formed (§33.9.12.12 [exec.when.all]):
Intent Proposal
Published 2026-05-08
Author(s) Andrzej Krzemieński
Audience
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Intent Proposal
Published 2026-05-11
Author(s) Maged Michael, Paul McKenney, Michael Wong
Audience
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Abstract This paper proposes adding `compare` and `compare_load` member functions to `std::atomic<T>`. These functions perform an atomic comparison of the atomic object's value with an expected value, following the same bitwise comparison semantics as `compare_exchange_strong`, but without writing a new value to the atomic object. The `compare_load` variant also updates the expected argument on failure. Th
Intent Proposal
Published 2026-02-22
Author(s) Bjarne Stroustrup
Audience ,
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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 Proposal
Published 2026-05-11
Author(s) Ian Petersen
Audience
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Abstract * **Separation of interface and** implementation; the primary need identified in this paper is the ability to separate *what* an async function does (its interface) from *how* it does it (its implementation). The problem with the existing senders is that their types reflect the fully composed computation they represent so it is impossible to achieve this separation with the status quo.
Intent Proposal
Published 2026-05-10
Author(s) Inbal Levi, Fabio Fracassi, Andreas Weis, Corentin Jabot
Audience
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Abstract This paper contains the decision polls that the C++ Library Evolution group will take in May 2026.
Intent Proposal
Published 2026-05-11
Author(s) Andreas Weis
Audience
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Abstract In C, a `’\0’` in a char array marks the end of the string. A C string is not just a string that has a `’\0’` at the end. It’s a string that *ends* *at* *the* *first* `’\0’` *character*.
Intent Proposal
Published 2026-05-12
Author(s) Nevin Liber
Audience
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Abstract Now that we have `try_*_back` in `inplace_vector`, we should add it to `vector` and explore adding it to other sequence containers that provide `push_back` and `emplace_back`.
Intent Proposal
Published 2026-05-12
Author(s) Andrew Drakeford
Audience , ,
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Abstract Blelloch [Blelloch1990] identifies `reduce`, `scan`, and `transform` as core parallel primitives. P4016R0 demonstrated that efficient, reproducible reduction is achievable using a tree-based abstract expression.
Intent Proposal
Published 2026-05-12
Author(s) Hans Boehm
Audience ,
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Abstract There has been a lot of discussion arguing that the C++23 spec essentially forces ODR violations. by implementing atomics as both a struct/class (in C++) and a scalar (in C) IMO, that depends on your perspective. If you view C code as also C++ code, then ODR violations in a combined C with C++ program make sense. This is the common view of C types in C++.
Intent Proposal
Published 2026-05-12
Author(s) Hans Boehm, Guy Davidson, Jan Schultke
Audience ,
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Abstract We propose the addition of the following struct. Actual wording is still left as future work (some of which can be taken from p3864). This is basically identical to P2746, except that we constrain operations to be IEEE conformant whenever is_iec_559 is `true`.
Intent Proposal
Published 2026-05-11
Author(s) Konstantin Varlamov
Audience ,
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Abstract This paper is a small followup to [P3471R4 “Standard Library Hardening”](https://wg21.link/P3471R4) and [P3697R1 “Minor additions to C++26 standard library hardening”](https://wg21.link/P3697) that proposes adding several hardened preconditions across the Library. The unifying theme is in fact a lack of a unifying theme; these are “miscellaneous” checks that don’t fit into a larger category. This
Intent Proposal
Published 2026-05-12
Author(s) Matthias Wippich, Murat Can Çağrı
Audience ,
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Abstract One of the oldest and most widely supported extensions to C++ is allowing `$` in identifiers. This feature's origins predate both standard C++ and standard C. As GCC notes in its [documentation](https://gcc.gnu.org/onlinedocs/gcc/Dollar-Signs.html):
Intent Proposal
Published 2026-05-11
Author(s) Daveed Vandevoorde, J. Garland, P. McKenney, R. Orr, B. Stroustrup, M. Wong
Audience
Revisions R0
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Abstract The above suggests priorities for standardization goals. However, we believe WG21’s work could also benefit from topical studies to gather data that will hopefully bring better understanding of the reality of C++. Examples include:
· source: open-std.org