# N4714 Editors' Report -- Programming Languages -- C++ 2017-11-27 Richard Smith (editor) (Google Inc) Dawn Perchik (co-editor) (Embarcadero Technologies Inc) Thomas Köppe (co-editor) (Google DeepMind) `` ## Acknowledgements Special thanks to Jens Maurer for performing many of the editorial fixes since N4700. Thanks to all those who have [submitted editorial issues](https://github.com/cplusplus/draft/wiki/How-to-submit-an-editorial-issue) and to those who have provided pull requests with fixes. ## New papers * [N4713](http://wg21.link/n4713) is the current working draft for C++20. It replaces [N4700](http://wg21.link/n4700). * N4714 is this Editors' Report. ## Motions incorporated into working draft ### Core working group motions CWG motion 1: [Core issue resolution](http://wg21.link/p0817r0) for 1 issue in "ready" status applied: * [2342](http://wg21.link/cwg2342) Reference `reinterpret_cast` and pointer-interconvertibility CWG motion 2: [Core issue resolutions](http://wg21.link/p0818r1) for 7 issues in "tentatively ready" status applied: * [1862](http://wg21.link/cwg1862) Determining "corresponding members" for friendship * [2177](http://wg21.link/cwg2177) Placement `operator delete` and parameter copies * [2305](http://wg21.link/cwg2305) Explicit instantiation of `constexpr` or `inline` variable template * [2307](http://wg21.link/cwg2307) Unclear definition of "equivalent to a nontype template parameter" * [2313](http://wg21.link/cwg2313) Redeclaration of structured binding reference variables * [2315](http://wg21.link/cwg2315) What is the "corresponding special member" of a variant member? * [2338](http://wg21.link/cwg2338) Undefined behavior converting to short enums with fixed underlying types CWG motion 3: [P0614R1 "Range-based `for` statements with initializer"](http://wg21.link/p0614r1) CWG motion 4: [P0588R1 "Simplifying implicit lambda capture"](http://wg21.link/p0588r1) CWG motion 5: [P0846R0 "ADL and function templates that are not visible"](http://wg21.link/p0846r0) CWG motion 6: [P0641R2 "Resolving core issue #1331"](http://wg21.link/p0641r2), resolving 1 core issue: * [1331](http://wg21.link/cwg1331) `const` mismatch with defaulted copy constructor CWG motion 7: [P0859R0 "Core issue 1581"](http://wg21.link/p0859r0), resolving 1 core issue: * [1581](http://wg21.link/cwg1581) When are `constexpr` member functions defined? CWG motion 8: [P0515R3 "Consistent comparison"](http://wg21.link/p0515r3) and [P0768R1 "Library support for the spaceship (comparison) operator"](http://wg21.link/p0768r1) CWG motion 9: [P0857R0 "Functionality gaps in constraints"](http://wg21.link/p0857r0) CWG motion 10: [P0692R1 "Access checking on specializations"](http://wg21.link/p0692r1) CWG motion 11: [P0624R2 "Default constructible and assignable stateless lambdas"](http://wg21.link/p0624r2) CWG motion 12: [P0767R1 "Deprecate POD"](http://wg21.link/p0767r1) CWG motion 13: [P0315R4 "Lambdas in unevaluated contexts"](http://wg21.link/p0315r4) ### Library working group motions LWG motion 1 and 2 apply to the Parallelism TS. LWG motion 3 applies to the Networking TS. LWG motion 4: [Library issue resolutions](http://wg21.link/p0815r0) for 24 issues in "Ready" or "Tentatively Ready" status applied: * [2870](http://wg21.link/lwg2870) Default value of parameter `theta` of `polar` should be dependent * [2935](http://wg21.link/lwg2935) What should `create_directories` do when `p` already exists but is not a directory? * [2941](http://wg21.link/lwg2941) [thread.req.timing] wording should apply to both member and namespace-level functions * [2944](http://wg21.link/lwg2944) [LWG 2905](http://wg21.link/lwg2905) accidentally removed requirement that construction of the deleter doesn't throw an exception * [2945](http://wg21.link/lwg2945) Order of template parameters in `optional` comparisons * [2948](http://wg21.link/lwg2948) `unique_ptr` does not define `operator<<` for stream output * [2950](http://wg21.link/lwg2950) `std::byte` operations are misspecified * [2952](http://wg21.link/lwg2952) `iterator_traits` should work for pointers to *cv* `T` * [2953](http://wg21.link/lwg2953) [LWG 2853](http://wg21.link/lwg2853) should apply to `deque::erase` too * [2964](http://wg21.link/lwg2964) Apparently redundant requirement for `dynamic_pointer_cast` * [2965](http://wg21.link/lwg2965) Non-existing `path::native_string()` in `filesystem_error::what()` specification * [2972](http://wg21.link/lwg2972) What is `is_trivially_destructible_v`? * [2976](http://wg21.link/lwg2976) Dangling `uses_allocator` specialization for `packaged_task` * [2977](http://wg21.link/lwg2977) `unordered_`*meow*`::merge()` has incorrect **Throws:** clause * [2978](http://wg21.link/lwg2978) Hash support for `pmr::string` and friends * [2979](http://wg21.link/lwg2979) `aligned_union` should require complete object types * [2980](http://wg21.link/lwg2980) Cannot `compare_exchange` empty pointers * [2981](http://wg21.link/lwg2981) Remove redundant deduction guides from standard library * [2982](http://wg21.link/lwg2982) Making `size_type` consistent in associative container deduction guides * [2988](http://wg21.link/lwg2988) Clause 32 cleanup missed one `typename` * [2993](http://wg21.link/lwg2993) `reference_wrapper` conversion from `T&&` * [2998](http://wg21.link/lwg2998) Requirements on function objects passed to {`forward_`,}`list`-specific algorithms * [3001](http://wg21.link/lwg3001) `weak_ptr::element_type` needs `remove_extent_t` * [3024](http://wg21.link/lwg3024) `variant`'s copies must be deleted instead of disabled via SFINAE LWG motion 5: [Library issue resolution](http://wg21.link/p0864r0) for 1 issue in "Immediate" status applied: * [2958](http://wg21.link/2958) Moves improperly defined as deleted LWG motion 6: [P0550R2 "Transformation trait `remove_cvref`"](http://wg21.link/p0550r2) LWG motion 7: [P0777R1 "Treating unnecessary `decay`"](http://wg21.link/p0777r1) LWG motion 8: [P0600R1 "`[[nodiscard]]` in the Library"](http://wg21.link/p0600r1) Do not try and apply LWG motion 9 to the working draft. That's impossible. Instead, only realize the truth. There is no LWG motion 9. LWG motion 10: [P0439R0 "Make `std::memory_order` a scoped enumeration"](http://wg21.link/p0439r0) LWG motion 11: [P0053R7 "Synchronized buffered `ostream`"](http://wg21.link/p0053r7) LWG motion 12: [P0653R2 "Utility to convert a pointer to a raw pointer"](http://wg21.link/p0653r2) LWG motion 13: [P0202R3 "Add `constexpr` modifiers to functions in `` and `` Headers"](http://wg21.link/p0202r3) LWG motion 14: [P0415R1 "`constexpr` for `std::complex`"](http://wg21.link/p0415r1) LWG motion 15: [P0718R2 "Atomic `shared_ptr`"](http://wg21.link/p0718r2) LWG motion 16: [P0020R6 "Floating point atomic"](http://wg21.link/p0020r6) LWG motion 17: [P0616R0 "De-pessimize legacy `` algorithms with `std::move`"](http://wg21.link/p0616r0) LWG motion 18: [P0457R2 "String prefix and suffix checking"](http://wg21.link/p0457r2) ## Notable editorial changes ### CWG motion 8 Instead of removing [operators] and adding a new section to [requirements], the existing stable name for this section is preserved. This section was moved to [description] rather than to [requirements], as it describes a notational device used for standard exposition. [alg.3way] added to [alg.sorting] rather than [alg.nonmodifying] to match existing `lexicographical_compare` functions. ### LWG motion 8 `[[nodiscard]]` was inadvertantly omitted from `deque::empty()` in the detailed wording changes (but was covered by the general description of the change). After consultation with LWG, this oversight has been corrected in the wording. ### LWG motion 10 All references to the existing `memory_order_*` enumerators throughout the working draft were updated to use the new scoped enumerator nmaes. ### LWG motion 11 Changes were made to the organization and presentation of the wording to fit better into the existing document. ### LWG motion 12 The requested addition to [pointer.traits.function] has been moved into a new subclause "Pointer traits optional members" and modified slightly to fit this new presentation, as it does not describe a member of the `pointer_traits` primary template. ### Text reorganization In an effort to conform to ISO drafting directives to avoid hanging paragraphs (text in subclauses that also contain further nested subclauses) and to remove excessive subclause structure, the following changes have been made: * [intro] and [basic] have been reorganized so that [intro] acts as an introduction to the standard document and [basic] introduces the basic concepts of the standard in an order closer to dependency order * [conv.rank] moved from [conv] to [basic.types], as it does not describe a conversion. * [expr] has additional subclause structure to partially resolve hanging paragraphs and generally improve its organization * [expr] has a new subclause describing properties of expressions, containing some of the prior hanging paragraphs from [expr], as well as [basic.lval] * [array], [util.sharedptr] Per-function subclauses have been merged into parent subclause. ### Changes in the style of specification * Code font is no longer used when referring to non-syntax properties of entities (even when those properties are derived from syntax). This applies to the terms "inline", "friend", "public", "protected", "private", "const object". We generally intend to use code font only when referring specifically to program syntax. * In library wording, template headers are formatted consistently with no space between the `template` keyword and the `<` token. Drafting for future standard changes should take the above into account. ### Index of library headers In order to keep the "Index of library names" focused on listing library names, index entries for library headers have been moved to a separate, new "Index of library headers". ## Minor editorial fixes A log of editorial fixes made to the working draft since N4700 is below. This list excludes changes that do not affect the body text or only affect whitespace or typeface. For a complete list including such changes (or for the actual deltas applied by these changes), consult the [draft sources on github](https://github.com/cplusplus/draft/compare/n4700...n4713). commit 903df06f3e67c9a52539892cb6844b55392c5331 Author: Thomas Köppe Date: Mon Nov 27 22:00:03 2017 +0000 [allocator.adaptor.syn] Delete duplicate declarations of relational operators commit cebfe0a09fb56ec33726559c8b6d006dc19e4ab7 Author: Jens Maurer Date: Wed Nov 15 23:18:22 2017 +0100 [temp.constr.order] In definition of 'subsumes', remove confusing introductory paragraph. commit 74df95e9e3fad1aa5844c281614bbfffb1cc6189 Author: Jens Maurer Date: Wed Nov 22 23:45:18 2017 +0100 [diff] Introduce numbered paragraphs commit e543af304e195ad301da272caa7ef12107077ac0 Author: Jens Maurer Date: Sat Nov 25 00:01:36 2017 +0100 [lib] Harmonize spacing for template headers. Use 'template'. Also remove space between two closing template brackets. commit b73e56f7a2b92449d9ec4938b01fa7014edad33a Author: Jens Maurer Date: Wed Nov 15 23:26:11 2017 +0100 [basic.link] Entities declared in an unnamed namespace never have external linkage. commit fc16d3133817701a780092cf6456722a40e27d28 Author: Jens Maurer Date: Sun Nov 19 23:11:51 2017 +0100 [temp.arg.explicit] Remove note obsoleted by P0846R0 commit d29bd8c6591fe74b095e5bd277f986462ba40b24 Author: Jens Maurer Date: Sun Nov 26 18:36:42 2017 +0100 [fs.op.funcs] Separate effects from returns. (#1848) commit e2457df32a6ee70417681de10be78eb815a0b22f Author: Jens Maurer Date: Mon Nov 20 10:23:18 2017 +0100 [complex.numbers] Use \xref for references to the C standard. commit bd2ce5c2d4ec26a5c412160ce5983149c510a131 Author: Jens Maurer Date: Tue Nov 21 23:35:02 2017 +0100 Create a new index for library headers and remove them from the index of library names. commit d1125303456c2305a72baebbb51d80151722f8ab Author: Jonathan Wakely Date: Thu Nov 23 14:33:32 2017 +0000 [basic.life],[mem.res.private],[mem.res.pool.mem],[mem.res.monotonic.buffer] fix cross-references commit 1d467a8a06cabd314e250a04ca9a4c81591d035a Author: Johel Ernesto Guerrero Peña Date: Thu Nov 23 15:31:45 2017 -0400 [func.require] Clarify which assignment operators commit 9dbbf9cbbe6994f7d4ad19098029e995eb34e1c3 Author: Johel Ernesto Guerrero Peña Date: Sat Nov 25 19:04:08 2017 -0400 [unord.req, fs.path.io] Fix "Effects: Equivalent to" styles (#1806) commit efdda2b9ca7f0ed78d7f134d8b1ca2e405610190 Author: Jens Maurer Date: Sat Nov 25 22:57:08 2017 +0100 [lib] Harmonize punctuation of 'Effects: Equivalent to' (#1815) commit 63ccd0513f6d9ac3555ca8becfcd7d15ed503522 Author: stbergmann Date: Sat Nov 25 03:33:31 2017 +0100 [basic.types] Add missing "be" in note (#1839) commit 9a8f4fde487200bcf4433facb0274f67d540617c Author: Jens Maurer Date: Sat Nov 25 03:29:09 2017 +0100 [lex.ccon] Align char16_t phrasing to UTF-8 one (#1847) commit 784f8c9980a74393ceaf201b343aa232a82113a4 Author: Thomas Köppe Date: Fri Nov 24 01:03:52 2017 +0000 [complex{,.special,.members}] Use injected-class-name in class definitions and itemdecls commit 877918fdc3e5223006b782d3c5959470bd7c02a8 Author: Jonathan Wakely Date: Fri Nov 24 00:57:49 2017 +0000 [allocator.requirements] Fix pointer_to expression and reinstate descriptive variable 'r' (#1656) commit 2ca4340d93ec4cd63c330303e5beef20db8604df Author: Jonathan Wakely Date: Thu Nov 23 22:48:22 2017 +0000 [vector.bool] Use injected-class-name in synopsis (#1844) commit 4eedcb0d29f7c3b143dc3492caecb9c608590e12 Author: Richard Smith Date: Wed Nov 22 19:26:28 2017 -0800 [diff.cpp17.library] Add Annex C entry for new headers and added since C++17. commit 9112c6aecc48e1a0deea1f9493de224a43689a87 Author: Aaron Ballman Date: Mon Mar 13 09:51:35 2017 -0400 Use the terms "single-object delete expression" and "array delete expression" as definitions, removing the italics when not appropriate. commit b3b8a19812829ab521958eed6b2f1a3411180cdb Author: Thomas Köppe Date: Sun Nov 19 22:17:17 2017 +0000 [structure.summary] Remove obsolete paragraph about Note(s): and Example(s): elements that we no longer provide Also restyle a manual Note: in [unord.req] to use the standard note environment. commit 8958e953fd2cd60bd02ed4fcd2c055eded6e0f4d Author: Thomas Köppe Date: Tue Nov 21 23:28:52 2017 +0000 [unord.req] Spell out the behaviour of cbegin/cend, remove ambiguous note commit b64354a7503c1cdc358d7f5dd1405ed903e170ef Author: Thomas Köppe Date: Wed Nov 22 12:10:00 2017 +0000 [depr.meta.types] Merge POD deprecation into existing type traits deprecation section and reorganize the section a bit commit 374252a76008ac0316320d2dd4e8652910539a97 Author: Jens Maurer Date: Wed Nov 22 01:01:39 2017 +0100 [util.sharedptr] Dissolve subclause and integrate contents into parent. (#1814) commit 75c0adccb38301f66979cc3c3ab5cd15a0a75a17 Author: Jens Maurer Date: Tue Nov 21 23:29:05 2017 +0100 [expr, over] Add cross-references for 'usual arithmetic conversions'. (#1804) commit 7670c1a8e025aa464fe5bebff7ae2626fb01b07f Author: Jens Maurer Date: Tue Feb 7 11:10:48 2017 +0100 [structure.specifications] Do not use library description macros in running text This avoids colons in running text and some bad spacing. commit deb9fb19a039dbcd943a5955064d8c0e3d55a45c Author: Alisdair Meredith Date: Sat Mar 4 06:46:30 2017 -1000 Consistent comma after e.g. and i.e. After grepping to determine the preferred idiom, it seems clear that the standard prefers to follow both e.g. and i.e. with a comma, rather than omit it. This patch applies that rule to the few places that were missing the comma. commit e1b92d6c125ef43e19915ba0b031baa2c6611c62 Author: Thomas Köppe Date: Tue Nov 21 18:01:18 2017 +0000 [over.match.best] Remove meaningless "i.e." commit 72b80b32c7ab185cc08eb72cf24ce6d839f7e6f3 Author: Thomas Köppe Date: Tue Nov 21 16:19:36 2017 +0000 [alg.partition] Use established terminology 'partitioned with respect to' commit b4a1e3c1c73531f3a61ae6e44abecab766e9c537 Author: Thomas Köppe Date: Tue Nov 21 15:52:31 2017 +0000 [binary.search] Formulate partitioning requirements in the same style as all the other related algorithms do commit b1fd50580cf389c61635a5767bf46b1b8823ce0c Author: Jens Maurer Date: Tue Nov 21 13:04:27 2017 +0100 [expr.compound] Expression operators do not 'return' results. (#1818) commit 68e53321ed7bf8505748e0f69947e21f9374d3a2 Author: Johel Ernesto Guerrero Peña Date: Tue Nov 21 08:02:52 2017 -0400 [strings.general] Use plural "string classes" (#1823) The summary even says "string classes", and now we also have the "string_view classes". commit a5c25539b2605d8e6817b43d48e359d24642d1b7 Author: Jens Maurer Date: Tue Nov 21 11:46:26 2017 +0100 [variant] Move 'Otherwise' to start of following bullet. (#1813) commit e13e3097e6c92f67b86458af9a3d4793b0aeb544 Author: Thomas Köppe Date: Tue Nov 21 01:49:37 2017 +0000 [utilities] Add missing charconv entry to summary table commit cbd25c4b3e6f83aaf2fa9fe894ff52b1f428a8c5 Author: Thomas Köppe Date: Sun Nov 12 00:37:09 2017 -0700 Hyphenate 'pointer-to-member' when it is an adjective and define the adjective. Fixes #1369. commit 801fb0ba013362cede5a9eaeae0da688e554d3ad Author: Jens Maurer Date: Sun Nov 12 06:51:19 2017 +0100 [conv.rank] Move from [conv] to [basic.types] (#1802) commit ff65cec7b977db1a6900b0321f10c91e152ab8d2 Author: Jens Maurer Date: Wed Nov 1 23:39:21 2017 +0100 Use 'trailing requires-clause' where the requires-clause in a template-head is not meant. Fixes #1672. commit 672bb6075cb0512a234b4f6bdd41f00cc01e6642 Author: Jens Maurer Date: Wed Apr 19 23:03:42 2017 +0200 [dcl.init] Clarify introduction Fixes #1615. commit 7c6f936298543387f2f17563f01e95fce904783d Author: Jens Maurer Date: Thu Nov 2 22:18:04 2017 +0100 [array] Dissolve single-item subclauses. Partially addresses #1242. commit 04c4e8338eadb18deb63354a95c2624ef5b3fbed Author: Jens Maurer Date: Sat Nov 11 19:34:18 2017 +0100 [intro.execution] Clarify full-expression in example. Fixes #1706. commit 2e25955ecf6a576c98590097ec76aa616495c466 Author: Jens Maurer Date: Sat Nov 11 07:29:23 2017 +0100 [expr] Add subclauses and adjust cross-references to [expr]. Also move [basic.lval] into [expr]. commit 87c88e99620ecbc3958dc0e06d86aa72806206c4 Author: Casey Carter Date: Sat Nov 11 21:48:25 2017 -0700 [algorithms.general] & [algorithm.syn] name "mutating sequence operations" consistently (#1801) Despite the stable name "alg.modifying.operations," the section is titled "Mutating sequence operations." commit 0963b3d26dcce7dff2b924e4d9d3daff0e1f50d6 Author: Jens Maurer Date: Sun Nov 12 05:32:46 2017 +0100 [lib] Harmonize introductory comments in synopses (#1775) Even if no section reference is given, make them lowercase and remove trailing colons. commit 6b6578cc415bf17b237a0889ef2dc53f4b392d02 Author: Jens Maurer Date: Sun Nov 12 05:30:40 2017 +0100 [locale.moneypunct.virtuals] Add reference to ISO 4217. (#1779) commit 49870469d0a3347b91e42faa9c931859e924e83e Author: Jens Maurer Date: Sun Nov 12 04:21:40 2017 +0100 [lib] Add hyphen to 'well-defined' (#1776) commit 982a456f176ca00409c6e514af932051dce2485f Author: Jens Maurer Date: Sat Nov 11 05:06:58 2017 +0100 [intro], [basic] Rearrange subclauses Fixes #1539. commit 301a71e35c49fafe2188736aff2631f36c81dd47 Author: Richard Smith Date: Fri Nov 10 23:55:37 2017 -0800 [basic.lookup.argdep] Correct xref to point to the normative invisible friend rule. commit 4f77c89e7635c8a9f361a0757c7765bcefeacd5e Author: Thomas Köppe Date: Thu Nov 9 17:33:33 2017 -0700 [over.built] Improve placeholder phrasing commit 24bfe67b857bc6634ffc796324999373352d6d72 Author: Thomas Köppe Date: Wed Nov 8 23:50:33 2017 -0700 [meta.endian] Clarify wording regarding size of scalar types commit 7a7d123584613a90cc64dbfb4b848807c3f085c8 Author: Johel Ernesto Guerrero Peña Date: Wed Nov 8 01:50:47 2017 -0400 [any.class] Revert dot to comma typo from bdff8687c (#1795) commit ee8aa525e65ada1f1949ebc9eb006af8b29f7e85 Author: Jonathan Wakely Date: Wed Nov 8 00:13:27 2017 +0000 [basic.ios.members], [streambuf.virt.put], [cmplx.over] replace enumerated lists with itemized commit 6ca5523589f8eb8d2843fe34386382a34064f41d Author: Jonathan Wakely Date: Tue Nov 7 23:24:36 2017 +0000 [fstream], [fs.class.directory_entry] qualify filesystem::path consistently commit b4acb0ca022f5b4e8a535a164c845ab87e312a1f Author: Richard Smith Date: Tue Nov 7 08:56:03 2017 -0800 [basic.def] Fix typo "braced-enclosed". commit b174bd63680803b18f1ebce4d743b13c257cd3bf Author: Thomas Köppe Date: Thu Nov 2 18:54:45 2017 +0000 [defns.referenceable] Remove duplicate 'an' commit f0b892320c609974270ccd415ecef081529e664f Author: Jens Maurer Date: Thu Nov 2 03:19:54 2017 +0100 [array.size] Remove full member declaration from itemdecl. (#1790) commit ea4b17a448b46671488b96812629d92c0c9c61be Author: Jens Maurer Date: Fri Oct 27 00:53:45 2017 +0200 [expr.prim.lambda.capture] Move discusssion of capture-by-reference of references to after the introduction of 'capture by reference'. Fixes #1785.