Add draft of Editors' Report for new working draft.

Author: zygoloid

papers/d4764.md

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+# D4764 Editors' Report -- Programming Languages -- C++
+
+2018-07-06  
+Richard Smith (editor) (Google Inc)  
+Thomas Köppe (co-editor) (Google DeepMind)  
+Jens Maurer (co-editor)  
+Dawn Perchik (co-editor) (Bright Side Computing, LLC)  
+`<[email protected]>`
+
+## Acknowledgements
+
+Special thanks to Casey Carter for supplying a pull request to merge
+[P0898R3](http://wg21.link/p0898r3) (LWG motion 28),
+and working with us on editorial cleanups within the
+12 pages of added text.
+
+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
+
+ * [N4762](http://wg21.link/n4762) is the current working draft for C++20. It replaces [N4750](http://wg21.link/n4750).
+ * N4764 is this Editors' Report.
+
+## Motions incorporated into working draft
+
+### Core working group motions
+
+CWG motion 1: [Core issue resolutions](http://wg21.link/p1113r0) for 6 issues in "ready" status applied:
+
+ * [2254](http://wg21.link/cwg2254) Standard-layout classes and bit-fields
+ * [2293](http://wg21.link/cwg2293) Requirements for *simple-template-id* used as a *class-name*
+ * [2294](http://wg21.link/cwg2294) Dependent `auto` static data members
+ * [2321](http://wg21.link/cwg2321) Conditional operator and cv-qualified class prvalues
+ * [2322](http://wg21.link/cwg2322) Substitution failure and lexical order
+ * [2339](http://wg21.link/cwg2339) Underspecified template arguments in structured bindings
+
+CWG motion 2: [Core issue resolutions](http://wg21.link/p1114r0) for 6 issues in "tentatively ready" status applied:
+
+ * [2233](http://wg21.link/cwg2233) Function parameter packs following default arguments
+ * [2249](http://wg21.link/cwg2249) *identifier*s and *id-expression*s
+ * [2285](http://wg21.link/cwg2285) Issues with structured bindings
+ * [2351](http://wg21.link/cwg2351) `void{}`
+ * [2356](http://wg21.link/cwg2356) Base class copy and move constructors should not be inherited
+ * [2359](http://wg21.link/cwg2359) Unintended copy initialization with designated initializers **(not a DR)**
+
+CWG motion 3: [P0806R2 "Deprecate implicit capture of `this` via `[=]`"](http://wg21.link/p0806r2)
+
+CWG motion 4: [P1042R1 `__VA_OPT__` wording clarifications"](http://wg21.link/p1042r1)
+
+CWG motion 5: [P0929R2 "Checking for abstract class types"](http://wg21.link/p0929r2) applied, resolving 2 core issues:
+
+ * [1640](http://wg21.link/cwg1640) Array of abstract instance of class template
+ * [1646](http://wg21.link/cwg1646) *decltype-specifier*s, abstract classes, and deduction failure
+
+CWG motion 6: [P0732R2 "Class types in non-type template parameters"](http://wg21.link/p0732r2)
+
+CWG motion 7 was not approved
+
+CWG motion 8: [P1025R1 "Update the reference to the Unicode standard"](http://wg21.link/p1025r1)
+
+CWG motion 9: [P0528R3 "The curious case of padding bits, featuring atomic compare-and-exchange"](http://wg21.link/p0528r3)
+
+CWG motion 10: [P0722R3 "Efficient sized delete for variable sized classes"](http://wg21.link/p0722r3)
+
+CWG motion 11: [P1064R0 "Allowing virtual function calls in constant expressions"](http://wg21.link/p1064r0)
+
+CWG motion 12: [P1008R1 "Prohibit aggregates with user-declared constructors"](http://wg21.link/p1008r1)
+
+CWG motion 13: [P1120R0 "Consistency improvements for `<=>` and other comparison operators"](http://wg21.link/p1120r0)
+
+CWG motion 14: [P0542R5 "Contract-based programming"](http://wg21.link/p0542r5) **see below**
+
+CWG motion 15: [P0941R2 "Feature-test macros"](http://wg21.link/p0941r2) **see below**
+
+CWG motion 16: [P0892R2 "`explicit(bool)`"](http://wg21.link/p0892r2)
+
+### Library working group motions
+
+LWG motions 1-5 apply to the Parallelism TS
+
+LWG motions 6 and 7 apply to the Reflection TS
+
+LWG motions 8 and 9 apply to the Coroutines TS
+
+LWG motion 10 applies to the Networking TS
+
+LWG motion 11: [Library issue resolutions](http://wg21.link/p1082r0) for 14 issues in "Ready" and "Tentatively Ready" status applied:
+
+ * [2139](http://wg21.link/lwg2139) What is a user-defined type? **see below**
+ * [2970](http://wg21.link/lwg2970) Return type of `std::visit` misspecified
+ * [3058](http://wg21.link/lwg3058) Parallel `adjacent_difference` shouldn't require creating temporaries
+ * [3062](http://wg21.link/lwg3062) Unnecessary `decay_t` in `is_execution_policy_v` should be `remove_cvref_t`
+ * [3067](http://wg21.link/lwg3067) `recursive_directory_iterator::pop` must invalidate
+ * [3074](http://wg21.link/lwg3074) Non-member functions for `valarray` should only deduce from the `valarray`
+ * [3076](http://wg21.link/lwg3076) `basic_string` CTAD ambiguity
+ * [3079](http://wg21.link/lwg3079) [LWG 2935](http://wg21.link/lwg2935) forgot to fix the `existing_p` overloads of `create_directory`
+ * [3080](http://wg21.link/lwg3080) Floating point `from_chars` pattern specification breaks round-tripping
+ * [3083](http://wg21.link/lwg3083) What should `ios::iword(-1)` do?
+ * [3094](http://wg21.link/lwg3094) [time.duration.io]p4 makes surprising claims about encoding
+ * [3100](http://wg21.link/lwg3100) Unnecessary and confusing "empty span" wording
+ * [3102](http://wg21.link/lwg3102) Clarify `span` `iterator` and `const_iterator` behavior
+ * [3104](http://wg21.link/lwg3104) Fixing `duration` division
+ * Resolution of [3071](http://wg21.link/lwg3071) (`read_until` still refers to
+   "input sequence") from P1082R0 was not part of this motion, as it applies to
+   the Networking TS.
+
+LWG motion 12: [Library issue resolution](http://wg21.link/p0475r1) for 1 issue applied:
+
+ * [2511](http://wg21.link/lwg2511) Guaranteed copy elision for piecewise construction
+
+LWG motion 13: [P0476R2 "Bit-casting object representations"](http://wg21.link/p0476r2)
+
+LWG motion 14: [P0788R3 "Standard library specification in a concepts and contracts world"](http://wg21.link/p0788r3)
+
+LWG motion 15 was not approved
+
+LWG motion 16: [P0458R2 "Checking for existence of an element in associative containers"](http://wg21.link/p0458r2)
+
+LWG motion 17: [P0759R1 "`fpos` requirements"](http://wg21.link/p0759r1)
+
+LWG motion 18: [P1023R0 "`constexpr` comparison operators for `std::array`"](http://wg21.link/p1023r0)
+
+LWG motion 19: [P0769R2 "Add `shift` to `<algorithm>`"](http://wg21.link/p0769r2)
+
+LWG motion 20: [P0887R1 "The `identity` metafunction"](http://wg21.link/p0887r1)
+
+LWG motion 21: [P0879R0 "`constexpr` for `swap` and `swap`-related functions"](http://wg21.link/p0879r0) applied, resolving 1 issue:
+
+ * [2800](http://wg21.link/lwg2800) `constexpr` `swap`
+
+LWG motion 22: [P0758R1 "Implicit conversion traits and utility functions"](http://wg21.link/p0758r1)
+
+LWG motion 23: [P0556R3 "Integral power-of-2 operations"](http://wg21.link/p0556r3)
+
+LWG motion 24: [P0019R8 "`atomic_ref`"](http://wg21.link/p0019r8)
+
+LWG motion 25: [P0935R0 "Eradicating unnecessarily explicit default constructors from the standard library"](http://wg21.link/p0935r0)
+
+LWG motion 26: [P0646R1 "Improving the return value of `erase`-like algorithms"](http://wg21.link/p0646r1)
+
+LWG motion 27: [P0619R4 "Reviewing deprecated facilities of C++17 for C++20"](http://wg21.link/p0619r4) **see below**
+
+LWG motion 28: [P0898R3 "Standard library concepts"](http://wg21.link/p0898r3) **see below**
+
+## Notable editorial changes
+
+### CWG motion 14
+
+Subclause structure and paragraph order of [dcl.attr.contracts] was reworked.
+Several normatively-redundant statements were converted to notes or removed.
+
+### CWG motion 15
+
+Multiple papers moved at this meeting included suggested feature-test macros.
+However, these were not presented as editing instructions, because we did not
+have feature-test macros in the standard wording yet. After consultation with
+CWG and LWG, the following feature test macros have been added in addition to
+those listed in CWG motion 15 (all with value `201806L`):
+
+ *  `__has_cpp_attribute(assert)`
+ *  `__has_cpp_attribute(ensures)`
+ *  `__has_cpp_attribute(expects)`
+ *  `__cpp_explicit_bool`
+ *  `__cpp_nontype_template_parameter_class`
+ *  `__cpp_lib_atomic_ref`
+ *  `__cpp_lib_bit_cast`
+ *  `__cpp_lib_concepts`
+ *  `__cpp_lib_constexpr_swap_algorithms`
+ *  `__cpp_lib_list_remove_return_type`
+
+### CWG motions 16 and 12
+
+CWG motion 16 would have us change wording that was deleted by CWG motion 12.
+The requested change in CWG motion 16 (from teletype "`explicit`" to body font "explicit")
+was ignored.
+
+### LWG motion 11: issue 2139
+
+The underlying text has changed between the drafting of the resolution to this
+issue and its application. We believe every requested edit has been applied;
+however, an additional use of "user-defined type" has been added to
+[namespace.std] that should likely also have been covered by this wording.
+It has *not* been changed.
+
+### LWG motions 13 and 23
+
+These motions both introduce a `<bit>` header, but the organizational structure
+suggested by motion 23 doesn't make sense for the functionality
+added by motion 13.
+The wording of motion 23 has been rearranged to fit into
+the structure established by motion 13.
+
+### LWG motions 16
+
+Added the new `contains` member function for associative containers to the list
+of member function templates that do not participate in overload resolution
+unless the comparator is transparent, after consultation with LWG.
+
+### LWG motions 19 and 21
+
+LWG motion 19 adds a `shift_right` algorithm to `<algorithm>`
+as a non-`constexpr` function template.
+
+LWG motion 21 instructs that we mark
+all non-parallel algorithms in `<algorithm>`
+as `constexpr`.
+Naturally, however,
+its proposed wording change does not list the `shift_right` algorithm.
+After consultation with LWG, `shift_right` has been marked `constexpr`
+to satisfy the intent of LWG motion 21.
+
+### LWG motion 27
+
+Synopses for
+`<ccomplex>`,
+`<cstdalign>`,
+`<cstdbool>`, and
+`<ctgmath>`
+were not removed;
+instead, they have been repurposed as synopses for
+`<complex.h>`,
+`<stdalign.h>`,
+`<stdbool.h>`, and
+`<tgmath.h>`.
+(The latter used to be defined in terms of the former,
+but can no longer be specified in that way.)
+Also introduced a synopsis for `<iso646.h>`.
+
+### LWG motion 28
+
+Clause labels shortened and simplified throughout.
+
+The single-item clauses [concept.movable], [concept.copyable],
+[concept.semiregular], and [concept.regular] have been merged into their
+parent, [concepts.object].
+
+The single-item clauses [concept.signed.int] and [concept.unsigned.int]
+have been merged into their parent, [concept.integral].
+
+Legacy concept names changed from Cpp98Something to Cpp17Something. Many of
+these concepts did not exist in C++98 (which in any case was revoked and
+replaced by C++03).
+
+Reworked "uniform random bit generator" requirements to describe them in terms
+of the UniformRandomBitGenerator concept.
+
+Removed "there need be no subsumption relationship" wording that is already
+implied by the core language rules for concepts.
+
+### Editorial paper [P1076R1 "Clause reorganization"](http://wg21.likn/p1076r1)
+
+The claue reorganization described in P1076R1 and discussed at the WG21
+Rapperswil meeting has been applied to the working draft, with the following
+modifications:
+
+[class.copy] was left containing only two paragraphs of text, neither of which
+had any normative impact. It has been removed.
+
+The top-level subclauses of [algorithms] have been reordered to make the
+description of the `<numeric>` header fit better into its structure.
+
+Several paragraphs of [class] describing various properties of classes have
+been moved into a new subclause [class.prop] "Properties of clases".
+
+### Removal of single-item subclauses
+
+The single-item subclauses
+[move.iter.op=] and
+[move.iter.op.const]
+have been merged into [move.iter.cons].
+
+The single-item subclauses
+[move.iter.op.star],
+[move.iter.op.ref], and
+[move.iter.op.index]
+have been merged into [move.iter.elem].
+
+The single-item subclauses
+[move.iter.op.+],
+[move.iter.op.-],
+[move.iter.op.incr],
+[move.iter.op.+=],
+[move.iter.op.decr], and
+[move.iter.op.-=]
+have been merged into [move.iter.nav].
+
+The now-empty [move.iter.ops] has been removed.
+
+## Minor editorial fixes
+
+A log of editorial fixes made to the working draft since N4750 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/n4750...n4762).
+