C++20

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Short description: 2020 edition of the C++ programming language standard


C++20 is a version of the ISO/IEC 14882 standard for the C++ programming language. C++20 replaced the prior version of the C++ standard, called C++17, and was later replaced by C++23.[1] The standard was technically finalized[2] by WG21 at the meeting in Prague in February 2020,[3] had its final draft version announced in March 2020,[4] was approved on 4 September 2020,[5][6] and published in December 2020.[7]

Features

C++20 adds more new major features than C++14 or C++17.[8] Changes that have been accepted into C++20 include:[9]

Language

  • concepts,[10] with terse syntax[11]
  • modules[12]
  • designated initializers[13] (based on the C99 feature, and common g++ extension)
  • [=, this] as a lambda capture[14]
  • template parameter lists on lambdas[15]
  • three-way comparison using the "spaceship operator", operator <=>
  • initialization of an additional variable within a range-based for statement[16]
  • lambdas in unevaluated contexts[17][18]
  • default constructible and assignable stateless lambdas[17][19]
  • allow pack expansions in lambda init-capture[17][20]
  • class types in non-type template parameters, also allowing string literals as template parameters[21]
  • removing the need for typename in certain circumstances[22]
  • new standard attributes no unique address,[23] likely and unlikely[24]
  • conditional explicit, allowing the explicit modifier to be contingent on a boolean expression[25]
  • expanded constexpr: virtual functions,[26] union,[27] try and catch,[28] dynamic_cast and typeid,[29] std::pointer_traits[30]
  • immediate functions using the new consteval keyword[31]
  • signed integers are now defined to be represented using two's complement (signed integer overflow remains undefined behavior)[32]
  • a revised memory model[33]
  • various improvements to structured bindings (interaction with lambda captures, static and thread_local storage duration)[34][35]
  • coroutines[36]
  • using on scoped enums[37]
  • constinit keyword[38]

Library

  • ranges (The One Ranges Proposal)[39]
  • std::make_shared and std::allocate_shared for arrays[40]
  • atomic smart pointers (such as std::atomic<shared_ptr<T>> and std::atomic<weak_ptr<T>>)[41]
  • std::to_address to convert a pointer to a raw pointer[42]
  • calendar and time-zone additions to <chrono>[43]
  • std::span, providing a view to a contiguous array (analogous to std::string_view but span can mutate the referenced sequence)[44]
  • std::erase and std::erase_if, simplifying element erasure for most standard containers[45]
  • <version> header[46]
  • std::bit_cast<> for type casting of object representations, with less verbosity than memcpy() and more ability to exploit compiler internals[47]
  • feature test macros[48]
  • various constexpr library bits[49]
  • smart pointer creation with default initialization[50]
  • contains-method for associative containers[51]
  • bit operations, such as leading/trailing zero/one count,[52] and log2 operations[53][54][55]
  • std::bind_front[56]

New and changed keywords

Many new keywords added (and the new "spaceship operator", operator <=>), such as concept, constinit,[38] consteval, co_await, co_return, co_yield, requires (plus changed meaning for export), and char8_t (for UTF-8 support).[57] And explicit can take an expression since C++20.[58] Most of the uses of the volatile keyword have been deprecated.[59]

In addition to keywords, there are identifiers with special meaning, including new import and module.

New attributes in C++20: likely, unlikely, and no unique address[60]

Removed and deprecated

Removed features:[61]

  • The C-derived headers <ccomplex>, <ciso646>, <cstdalign>, <cstdbool> and <ctgmath> were removed, as they serve no purpose in C++. (The corresponding <*.h> headers remain, for compatibility with C.)
  • The use of throw() as an exception specification was removed.
  • Some previously deprecated library features were removed, including std::uncaught_exception, std::raw_storage_iterator, std::is_literal_type, std::is_literal_type_v, std::result_of and std::result_of_t.

Deprecated features:

  • Use of comma operator in subscript expressions has been deprecated[62]
  • (most of) volatile has been deprecated[59]

Published as Technical Specifications

  • Parallelism TS v2[63] (including task blocks[64])
  • Reflection TS v1[65]
  • Networking TS v1[66]

Deferred to a later standard

  • Contracts – a new study group (SG21) has been formed to work on a new proposal[67]
  • Reflection[68][69]
  • Metaclasses[70]
  • Executors[71]
  • Networking extensions,[72][73] including async, basic I/O services, timers, buffers and buffer-oriented streams, sockets, and Internet protocols (blocked by executors)
  • Properties[74]
  • Extended futures[75]

Compiler support

Full support[76]

  • Visual Studio 2019 supports all C++20 features through its /std:c++latest option, as of version 16.10.0.[77] An option /std:c++20 to enable C++20 mode is added in version 16.11.0.[78][79]

Microsoft's compiler does not just support Windows, also Linux (and e.g. Android and iOS), while it then requires the "Visual C++ for Linux Development extension".[80]

Partial

  • Clang has partial C++20 support that can be enabled with the option -std=c++20 (version 10 and later) or -std=c++2a (version 9 and earlier).[81]
  • EDG started implementing C++20 features in version 5.0 and as of version 6.1 supports most C++20 core language features.[82]
  • GCC added partial, experimental C++20 support in 2017[83] in version 8 through the option -std=c++2a. Like Clang, GCC replaced this option with -std=c++20 in version 10. It also has an option to enable GNU extensions in addition to the experimental C++20 support, -std=gnu++20.[84]

History

Changes applied to the C++20 working draft in July 2017 (Toronto) include:[85]

  • concepts (what made it into the standard is a cut-down version; also described as "Concepts Lite"[86])
  • designated initializers
  • [=, this] as a lambda capture
  • template parameter lists on lambdas
  • std::make_shared and std::allocate_shared for arrays

Changes applied to the C++20 working draft in the fall meeting in November 2017 (Albuquerque) include:[87][88]

  • three-way comparison using the "spaceship operator", operator <=>
  • initialization of an additional variable within a range-based for statement
  • lambdas in unevaluated contexts
  • default constructible and assignable stateless lambdas
  • allow pack expansions in lambda init-capture
  • string literals as template parameters
  • atomic smart pointers (such as std::atomic<shared_ptr<T>> and std::atomic<weak_ptr<T>>)
  • std::to_address to convert a pointer to a raw pointer

Changes applied to the C++20 working draft in March 2018 (Jacksonville) include:[89]

  • removing the need for typename in certain circumstances
  • new standard attributes no unique address, likely and unlikely
  • calendar and time-zone additions to <chrono>
  • std::span, providing a view to a contiguous array (analogous to std::string_view but span can mutate the referenced sequence)
  • <version> header

Changes applied to the C++20 working draft in the summer meeting in June 2018 (Rapperswil) include:[90]

  • contracts (later deferred to a later standard)[91]
  • feature test macros
  • bit-casting of object representations, with less verbosity than memcpy() and more ability to exploit compiler internals
  • conditional explicit, allowing the explicit modifier to be contingent on a boolean expression
  • constexpr virtual functions

Changes applied to the C++20 working draft in the fall meeting in November 2018 (San Diego) include:[92]

  • ranges (The One Ranges Proposal)
  • concept terse syntax
  • constexpr union, try and catch, dynamic_cast, typeid and std::pointer_traits.
  • various constexpr library bits
  • immediate functions using the new consteval keyword
  • signed integers are now defined to be represented using two's complement (signed integer overflow remains undefined behavior)
  • refinements of the contracts facility (access control in contract conditions)[93] (see list of features deferred to a later standard)
  • a revised memory model
  • smart pointer creation with default initialization

Changes applied to the C++20 working draft in the winter meeting in February 2019 (Kona) include:[94][95][96]

  • coroutines
  • modules
  • various improvements to structured bindings (interaction with lambda captures, static and thread_local storage duration)

Changes applied to the C++20 working draft in the summer meeting in July 2019 (Cologne) include:[97][98][99][100]

  • contracts were removed (see list of features deferred to a later standard)[101]
  • use of comma operator in subscript expressions has been deprecated[62]
  • constexpr additions (trivial default initialization,[102] unevaluated inline-assembly[103])
  • using scoped enums[37]
  • various changes to the spaceship operator[104][105]
  • DR: minor changes to modules[106]
  • constinit keyword
  • changes to concepts (removal of -> Type return-type-requirements[107])
  • (most of) volatile has been deprecated[59]
  • DR: nodiscard effects on constructors[108]
  • The new standard library concepts will not use PascalCase (rather standard_case, as the rest of the standard library)[109]
  • text formatting (std::format, [110][111] chrono integration,[112] corner case fixes[113])
  • bit operations[52]
  • constexpr INVOKE[114]
  • math constants[115]
  • consistency additions to atomics (std::atomic_ref<T>,[116] std::atomic<std::shared_ptr<T>>[117])
  • add the <=> operator to the standard library[118]
  • header units for the standard library[119]
  • synchronization facilities[120] (merged from: Efficient atomic waiting and semaphores,[121] latches and barriers,[122] Improving atomic_flag,[123] Don't Make C++ Unimplementable On Small CPUs[124])
  • std::source_location[125]
  • constexpr containers (std::string,[126] std::vector[127])
  • std::stop_token and joining thread (std::jthread)[128]

Changes applied during the NB comment resolution in the fall meeting in November 2019 (Belfast) include:[129][130][131][132]

  • Class Types in Non-Type Template Parameters (NTTP): The restriction of no user-defined operator== allowed has been removed as the meaning of template argument equality has been divorced from operator==.[133] This allows also for array members in class-type NTTP.
  • Floating-point types,[134] pointers and references and unions and union-like classes (class types containing anonymous unions) are now allowed as NTTP.
  • Function identity now also includes trailing requires-clauses (P1971)
  • Constrained non-template functions have been removed
  • <compare> is now available in freestanding implementations[135]
  • std::spans typedef was changed from index_type to size_type to be consistent with the rest of the standard library[136]
  • Concept traits have been renamed to follow the renaming of the concepts as a result from the Cologne meeting
  • Several fixes and additions to ranges (P1456R1: Move-only views,[137] P1391R4: Range constructor for std::string_view (constructor from iterator-pair of characters),[138] P1394R4: Range constructor for std::span<ref>,[139] P1870R1: forwarding-range<T> is too subtle[140])
  • Initialization for std::atomic<T> has been changed to make it work with default and list initialization,[141] std::latch and std::barrier can now report the maximum number of threads that the implementation supports through the new member function max()
  • std::weak_equality and std::strong_equality have been removed as they are not used anymore
  • Algorithms in <numeric> have been made constexpr
  • Missing feature-test macros for new or changed features of C++20 have been added[142]

References

  1. ↑ "The Standard". https://isocpp.org/std/the-standard. Retrieved 7 September 2020. 
  2. ↑ Sutter, Herb (2019-10-01). "P1000R3: C++ IS schedule". https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2019/p1000r3.pdf. 
  3. ↑ Dusíková, Hana (2019-11-06). "N4817: 2020 Prague Meeting Invitation and Information". https://open-std.org/JTC1/SC22/WG21/docs/papers/2019/n4817.pdf. 
  4. ↑ "N4859 Editors' Report -- Programming Languages -- C++". https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2020/n4859.html. 
  5. ↑ "Current Status". https://isocpp.org/std/status. Retrieved 7 September 2020. 
  6. ↑ "C++20 Approved -- Herb Sutter". https://isocpp.org/blog/2020/09/cpp20-approved-herb-sutter. Retrieved 8 September 2020. 
  7. ↑ "ISO/IEC 14882:2020". https://www.iso.org/standard/79358.html. 
  8. ↑ "Why does the C++ standard ship every three years?". 13 July 2019. https://herbsutter.com/2019/07/13/draft-faq-why-does-the-c-standard-ship-every-three-years/. 
  9. ↑ "P0592R0: To boldly suggest an overall plan for C++20". https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2017/p0592r0.html. 
  10. ↑ "P0606R0: Concepts Are Ready". https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2017/p0606r0.pdf. 
  11. ↑ "P1141R1 - Yet another approach for constrained declarations". http://open-std.org/JTC1/SC22/WG21/docs/papers/2018/p1141r1.html. 
  12. ↑ "N4720: Working Draft, Extensions to C++ for Modules". https://isocpp.org/files/papers/n4720.pdf. 
  13. ↑ "Designated Initialization Wording". https://wg21.link/p0329. 
  14. ↑ Thomas Köppe. "Allow lambda capture [=, this"]. https://wg21.link/p0409. 
  15. ↑ "Familiar template syntax for generic lambdas". https://wg21.link/p0428. 
  16. ↑ "Range-based for statements with initializer". https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2017/p0614r0.html. 
  17. ↑ 17.0 17.1 17.2 "Trip Report: C++ Standards Meeting in Albuquerque, November 2017" (in en-US). There's Waldo!. 2017-11-20. https://botondballo.wordpress.com/2017/11/20/trip-report-c-standards-meeting-in-albuquerque-november-2017/. 
  18. ↑ "Wording for lambdas in unevaluated contexts". https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2017/p0315r4.pdf. 
  19. ↑ "Default constructible and assignable stateless lambdas". https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2017/p0624r2.pdf. 
  20. ↑ "Pack expansion in lambda init-capture". https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2017/p0780r0.html. 
  21. ↑ "Class Types in Non-Type Template Parameters". 2018-06-06. https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2018/p0732r2.pdf. 
  22. ↑ "Down with typename!". https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2018/p0634r3.html. 
  23. ↑ "Language support for empty objects". https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2018/p0840r2.html. 
  24. ↑ "Proposed wording for likely and unlikely attributes (Revision 5)". https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2018/p0479r5.html. 
  25. ↑ "explicit(bool)". https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2018/p0892r2.html. 
  26. ↑ "Allowing Virtual Function Calls in Constant Expressions". https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2018/p1064r0.html. 
  27. ↑ "P1330R0 - Changing the active member of a union inside constexpr". https://wg21.link/p1330. 
  28. ↑ "P1002R0 - Try-catch blocks in constexpr functions". https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2018/p1002r0.pdf. 
  29. ↑ "P1327R0 - Allowing dynamic_cast, polymorphic typeid in Constant Expressions". https://wg21.link/p1327. 
  30. ↑ "P1006R1 - Constexpr in std::pointer_traits". https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2018/p1006r1.pdf. 
  31. ↑ "P1073R2 - Immediate functions". https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2018/p1073r2.html. 
  32. ↑ "P1236R0: Alternative Wording for P0907R4 Signed Integers are Two's Complement". https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2018/p1236r0.html. 
  33. ↑ "P0668R4: Revising the C++ memory model". https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2018/p0668r4.html. 
  34. ↑ "P1091R1: Extending structured bindings to be more like variable declarations". https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2018/p1091r1.html. 
  35. ↑ "P1091R2: Extending structured bindings to be more like variable declarations". https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2018/p1091r2.html. 
  36. ↑ "N4649: Working Draft, Technical Specification for C++ Extensions for Coroutines". https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2017/n4649.pdf. 
  37. ↑ 37.0 37.1 "P1099R5: Using Enum". 2019-07-20. http://open-std.org/JTC1/SC22/WG21/docs/papers/2019/p1099r5.html. 
  38. ↑ 38.0 38.1 "P1143R2: Adding the constinit keyword". 2019-07-20. http://open-std.org/JTC1/SC22/WG21/docs/papers/2019/p1143r2.html. 
  39. ↑ "P0896R3". https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2018/p0896r3.pdf. 
  40. ↑ "Extending make_shared to Support Arrays". https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2017/p0674r1.html. 
  41. ↑ Meredith, Alisdair; Sutter, Herb. "Revising atomic_shared_ptr for C++20". ISO. https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2017/p0718r2.html. Retrieved 27 December 2018. 
  42. ↑ "Utility to convert a pointer to a raw pointer". https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2017/p0653r2.html. 
  43. ↑ "Extending <chrono> to Calendars and Time Zones". https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2018/p0355r7.html. 
  44. ↑ "span: bounds-safe views for sequences of objects". http://wg21.link/p0122. 
  45. ↑ "Adopt Consistent Container Erasure from Library Fundamentals 2 for C++20". 2018-10-04. https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2018/p1209r0.html. 
  46. ↑ Alan Talbot. "<version>". http://wg21.link/p0754. 
  47. ↑ "Bit-casting object representations". https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2018/p0476r2.html. 
  48. ↑ "Integrating feature-test macros into the C++ WD (rev. 2)". https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2018/p0941r2.html. 
  49. ↑ "P1032R1 - Misc constexpr bits". https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2018/p1032r1.html. 
  50. ↑ "Smart pointer creation with default initialization". https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2018/p1020r1.html. 
  51. ↑ "P0458R2: Checking for Existence of an Element in Associative Containers". https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2018/p0458r2.html. 
  52. ↑ 52.0 52.1 "P0553R4: Bit operations". 2019-07-20. http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2019/p0553r4.html. 
  53. ↑ "P0556R3: Integral power-of-2 operations". 2018-06-06. https://wg21.link/p0556r3. 
  54. ↑ "P1355R2 Exposing a narrow contract for ceil2". 2019-06-11. https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2019/p1355r2.html. 
  55. ↑ "On the names of low-level bit manipulation functions". 2020-02-11. https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2020/p1956r1.pdf. 
  56. ↑ Tomasz Kamiński (2017-11-09). "Simplified partial function application". https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2017/p0356r3.html. 
  57. ↑ "C++ keywords - cppreference.com". https://en.cppreference.com/w/cpp/keyword. 
  58. ↑ "explicit specifier - cppreference.com". https://en.cppreference.com/w/cpp/language/explicit. 
  59. ↑ 59.0 59.1 59.2 "P1152R4: Deprecating volatile". 2019-07-20. http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2019/p1152r3.html. 
  60. ↑ "attribute specifier sequence(since C++11) - cppreference.com". https://en.cppreference.com/w/cpp/language/attributes. 
  61. ↑ "Working Draft, Standard for Programming Language C++ (Annex C, §C.1)". http://open-std.org/JTC1/SC22/WG21/docs/papers/2020/n4861.pdf. 
  62. ↑ 62.0 62.1 "P1161R2: Deprecate uses of the comma operator in subscripting expressions". https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2019/p1161r2.html. 
  63. ↑ "C++ Extensions for Parallelism Version 2". https://wg21.link/N4793. 
  64. ↑ "Task Blocks". 3 March 2017. http://www.modernescpp.com/index.php/task-blocks. 
  65. ↑ "C++ Extensions for Reflection". https://wg21.link/N4818. 
  66. ↑ "C++ Extensions for Networking". https://wg21.link/N4711. 
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  68. ↑ "Reflections on the reflection proposals - Meeting C++" (in en). https://meetingcpp.com/index.php/br/items/reflections-on-the-reflection-proposals.html. 
  69. ↑ "Static reflection". https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2018/p0194r6.html. 
  70. ↑ Herb Sutter. "Metaclasses". https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2017/p0707r0.pdf. 
  71. ↑ "A Unified Executors Proposal for C++". https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2019/p0443r10.html. 
  72. ↑ "N4771: Working Draft, C++ Extensions for Networking". https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2018/n4771.pdf. 
  73. ↑ "ISO/IEC TS 19216:2018 Programming Languages -- C++ Extensions for Networking". https://www.iso.org/standard/64030.html. 
  74. ↑ "A General Property Customization Mechanism". https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2019/p1393r0.html. 
  75. ↑ "A Unified Futures Proposal for C++". https://wg21.link/P1054. 
  76. ↑ "C++ compiler support - cppreference.com". https://en.cppreference.com/w/cpp/compiler_support. 
  77. ↑ jawiddis. "Visual Studio 2019 version 16.10 Release Notes" (in en-us). https://docs.microsoft.com/en-us/visualstudio/releases/2019/release-notes-v16.10#16.10.0. 
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  79. ↑ Visual Studio documentation for Microsoft C++, Microsoft Docs, 2022-04-19, https://github.com/MicrosoftDocs/cpp-docs/blob/578dd21279a897661686617375dff80f1eb2f40c/docs/overview/cpp-conformance-improvements.md, retrieved 2022-04-19 
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  83. ↑ "Andrew Sutton - [PATCH Add -std=c++2a"]. https://gcc.gnu.org/legacy-ml/gcc-patches/2017-07/msg01234.html. 
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  85. ↑ Herb Sutter (15 July 2017). "Trip report: Summer ISO C++ standards meeting (Toronto)". https://herbsutter.com/2017/07/15/trip-report-summer-iso-c-standards-meeting-toronto/. 
  86. ↑ "Concepts Lite: Constraining Templates with Predicates". 2013-02-24. https://isocpp.org/blog/2013/02/concepts-lite-constraining-templates-with-predicates-andrew-sutton-bjarne-s. 
  87. ↑ Herb Sutter (11 November 2017). "Trip report: Fall ISO C++ standards meeting (Albuquerque)". https://herbsutter.com/2017/11/11/trip-report-fall-iso-c-standards-meeting-albuquerque/. 
  88. ↑ Smith, Richard; Perchik, Dawn; Köppe, Thomas. "N4714 Editors' Report -- Programming Languages -- C++". GitHub. https://github.com/cplusplus/draft/blob/master/papers/n4714.md. Retrieved 27 December 2018. 
  89. ↑ Botond Ballo (28 March 2018). "Trip Report: C++ Standards Meeting in Jacksonville, March 2018". https://botondballo.wordpress.com/2018/03/28/trip-report-c-standards-meeting-in-jacksonville-march-2018/. 
  90. ↑ Herb Sutter (2 July 2018). "Trip report: Summer ISO C++ standards meeting (Rapperswil)". https://herbsutter.com/2018/07/02/trip-report-summer-iso-c-standards-meeting-rapperswil/. 
  91. ↑ "Support for contract based programming in C++". https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2018/p0542r5.html. 
  92. ↑ fall meeting in November 2018
  93. ↑ "P1289R0 - Access control in contract conditions". https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2018/p1289r0.pdf. 
  94. ↑ winter meeting in February 2019
  95. ↑ "r/cpp - 2019-02 Kona ISO C++ Committee Trip Report (C++20 design is complete; Modules in C++20; Coroutines in C++20; Reflection TS v1 published; work begins on a C++ Ecosystem Technical Report)" (in en). 23 February 2019. https://www.reddit.com/r/cpp/comments/au0c4x/201902_kona_iso_c_committee_trip_report_c20/. 
  96. ↑ "Trip report: Winter ISO C++ standards meeting (Kona)" (in en). 2019-02-23. https://herbsutter.com/2019/02/23/trip-report-winter-iso-c-standards-meeting-kona/. 
  97. ↑ "2019 Cologne Meeting Invitation and Information". https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2018/n4783.pdf. 
  98. ↑ "r/cpp - 2019-07 Cologne ISO C++ Committee Trip Report — 🚀 The C++20 Eagle has Landed 🚀 (C++20 Committee Draft shipped; Contracts Moved From C++20 to a Study Group; 'std::format' in C++20; C++20 Synchronization Library)" (in en). 20 July 2019. https://www.reddit.com/r/cpp/comments/cfk9de/201907_cologne_iso_c_committee_trip_report_the/. 
  99. ↑ Botond Ballo (26 July 2019). "Trip Report: C++ Standards Meeting in Cologne, July 2019". https://botondballo.wordpress.com/2019/07/26/trip-report-c-standards-meeting-in-cologne-july-2019/. 
  100. ↑ Sutter, Herb (20 July 2019). "Trip report: Summer ISO C++ standards meeting (Cologne)". https://herbsutter.com/2019/07/20/trip-report-summer-iso-c-standards-meeting-cologne/. 
  101. ↑ Josuttis, Nicolai. "P1823R0: Remove Contracts from C++20". https://open-std.org/JTC1/SC22/WG21/docs/papers/2019/p1823r0.pdf. 
  102. ↑ "Permitting trivial default initialization in constexpr contexts". https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2019/p1331r1.pdf. 
  103. ↑ "P1668R1: Enabling Constexpr Intrinsics By Permitting Unevaluated inline-asm in Constexpr Functions". http://open-std.org/JTC1/SC22/WG21/docs/papers/2019/p1668r1.html. 
  104. ↑ "P1186R3: When do you actually use <=>?". 2019-07-20. http://open-std.org/JTC1/SC22/WG21/docs/papers/2019/p1186r3.html. 
  105. ↑ "P1630R1: Spaceship needs a tune-up". 2019-07-20. http://open-std.org/JTC1/SC22/WG21/docs/papers/2019/p1630r1.html. 
  106. ↑ "P1766R1: Mitigating minor modules maladies". 2019-07-20. http://open-std.org/JTC1/SC22/WG21/docs/papers/2019/p1766r1.html. 
  107. ↑ "P1452R2: On the non-uniform semantics of return-type-requirements". 2019-07-20. http://open-std.org/JTC1/SC22/WG21/docs/papers/2019/p1452r2.html. 
  108. ↑ "P1771R1: nodiscard for constructors". 2019-07-20. http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2019/p1771r1.pdf. 
  109. ↑ "P1754R1: Rename concepts to standard_case for C++20, while we still can". 2019-07-20. http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2019/p1754r1.pdf. 
  110. ↑ "P0645R10: Text Formatting". 2019-07-20. http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2019/p0645r10.html. 
  111. ↑ "std::format in C++20". 2019-07-23. http://www.zverovich.net/2019/07/23/std-format-cpp20.html. 
  112. ↑ "P1361R2: Integration of chrono with text formatting". 2019-07-20. http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2019/p1361r2.pdf. 
  113. ↑ "P1652R1: Printf corner cases in std::format". 2019-07-20. http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2019/p1652r1.html. 
  114. ↑ "P1965R2: constexpr INVOKE". 2019-07-20. http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2019/p1065r2.html. 
  115. ↑ "P0631R8: Math Constants". 2019-07-20. http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2019/p0631r8.pdf. 
  116. ↑ "P1643R1: Add wait/notify to atomic_ref<T>". 2019-07-20. http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2019/p1643r1.html. 
  117. ↑ "P1664R0: Add wait/notify to atomic<shared_ptr<T>>". 2019-07-20. http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2019/p1644r0.html. 
  118. ↑ "P1614R2: The Mothership has Landed - Adding <=> to the Library". 2019-07-20. http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2019/p1614r2.html. 
  119. ↑ "P1502R1: Standard library header units for C++20". 2019-07-20. http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2019/p1502r1.html. 
  120. ↑ "P1135R6: The C++20 Synchronization Library". 2019-07-20. http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2019/p1135r6.html. 
  121. ↑ "P0514R4: Efficient concurrent waiting for C++20". http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2018/p0514r4.pdf. 
  122. ↑ "P0666R2: Revised Latches and Barriers for C++20". http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2018/p0666r2.pdf. 
  123. ↑ "P0995R1: Improving atomic_flag". http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2018/p0995r1.html. 
  124. ↑ "P1285R0: Don't Make C++ Unimplementable On Small CPUs". http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2018/p1258r0.html. 
  125. ↑ "P1208R6: Adopt source_location from Library Fundamentals V3 for C++20". http://open-std.org/JTC1/SC22/WG21/docs/papers/2019/p1208r6.pdf. 
  126. ↑ "P0980R1: Making std::string constexpr". http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2019/p0980r1.pdf. 
  127. ↑ "P1004R2: Making std::vector constexpr". http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2019/p1004r2.pdf. 
  128. ↑ "P0660R10: Stop Token and Joining Thread". http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2019/p0660r10.pdf. 
  129. ↑ fall meeting in November 2019
  130. ↑ "r/cpp - 2019-11 Belfast ISO C++ Committee Trip Report — Started Processing Feedback on the C++20 Committee Draft; ABI Review Group Formed" (in en-US). 9 November 2019. https://www.reddit.com/r/cpp/comments/dtuov8/201911_belfast_iso_c_committee_trip_report/. 
  131. ↑ Sutter, Herb (2019-11-09). "Trip report: Autumn ISO C++ standards meeting (Belfast)" (in en). https://herbsutter.com/2019/11/09/trip-report-autumn-iso-c-standards-meeting-belfast/. 
  132. ↑ botondballo (2019-11-15). "Trip Report: C++ Standards Meeting in Belfast, November 2019" (in en). https://botondballo.wordpress.com/2019/11/15/trip-report-c-standards-meeting-in-belfast-november-2019/. 
  133. ↑ "P1907R0: Inconsistencies with non-type template parameters". 2019-10-07. http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2019/p1907r0.html. 
  134. ↑ "P1714: NTTP are incomplete without float, double, and long double! (Revision 1)". 2019-07-19. http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2019/p1714r1.html. 
  135. ↑ "P1855R=: Make <compare> freestanding". 2019-10-05. http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2019/p1855r0.html. 
  136. ↑ "P1872R0: span should have size_type not index_type". 2019-09-16. http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2019/p1872r0.pdf. 
  137. ↑ "P1456: Move-only views". 2019-01-25. http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2019/p1456r0.pdf. 
  138. ↑ "P1391: Range constructor for std::string_view". http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2019/p1391r4.pdf. 
  139. ↑ "P1394: Range constructor for std::span". 2019-08-02. http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2019/p1394r3.pdf. 
  140. ↑ "P1870R1: forwarding-range<T> is too subtle". 6 October 2019. http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2019/p1870r0.html. 
  141. ↑ "P0883: Fixing Atomic Initialization". 2018-06-05. http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2018/p0883r1.pdf. 
  142. ↑ "Missing feature-test macros 2018-2019". 2019-10-06. http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2019/p1902r0.html. 

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