Merge 2022-02 LWG Motion 1

P2531R0 C++ Standard Library Issues

This excludes LWG3616, which was already applied editorially
as 8753efa.

Author: tkoeppe

source/atomics.tex

@@ -2801,6 +2801,7 @@
     bool is_lock_free() const noexcept;
 
     constexpr atomic() noexcept;
+    constexpr atomic(nullptr_t) noexcept : atomic() { }
     atomic(shared_ptr<T> desired) noexcept;
     atomic(const atomic&) = delete;
     void operator=(const atomic&) = delete;

source/containers.tex

@@ -7156,18 +7156,22 @@
 \end{itemdecl}
 
 \begin{itemdescr}
+\pnum
+Let \tcode{comp} be \tcode{less<>{}} for the first two overloads.
+
 \pnum
 \expects
-\tcode{*this} and \tcode{x} are both sorted with respect to
-the comparator \tcode{operator<} (for the first two overloads) or
-\tcode{comp} (for the last two overloads), and
+\tcode{*this} and \tcode{x} are both sorted
+with respect to the comparator \tcode{comp}, and
 \tcode{get_allocator() == x.get_allocator()} is \tcode{true}.
 
 \pnum
 \effects
-Merges the two sorted ranges \tcode{[begin(), end())} and
-\tcode{[x.begin(), x.end())}. \tcode{x} is empty after the merge. If an
-exception is thrown other than by a comparison there are no effects.
+If \tcode{addressof(x) == this}, there are no effects.
+Otherwise, merges
+the two sorted ranges \range{begin()}{end()} and \range{x.begin()}{x.end()}.
+The result is a range
+that is sorted with respect to the comparator \tcode{comp}.
 Pointers and references to the moved elements of \tcode{x} now refer to those same elements
 but as members of \tcode{*this}. Iterators referring to the moved elements will continue to
 refer to their elements, but they now behave as iterators into \tcode{*this}, not into
@@ -7176,11 +7180,15 @@
 \pnum
 \complexity
 At most \tcode{distance(begin(),
-end()) + distance(x.begin(), x.end()) - 1} comparisons.
+end()) + distance(x.begin(), x.end()) - 1} comparisons
+if \tcode{addressof(x) != this}; otherwise, no comparisons are performed.
 
 \pnum
 \remarks
 Stable\iref{algorithm.stable}.
+If \tcode{addressof(x) != this}, \tcode{x} is empty after the merge.
+No elements are copied by this operation.
+If an exception is thrown other than by a comparison, there are no effects.
 \end{itemdescr}
 
 \indexlibrarymember{sort}{forward_list}%
@@ -7857,40 +7865,39 @@
 \end{itemdecl}
 
 \begin{itemdescr}
+\pnum
+Let \tcode{comp} be \tcode{less<>{}} for the first two overloads.
+
 \pnum
 \expects
-Both the list and the argument list
-shall be sorted with respect to
-the comparator \tcode{operator<} (for the first two overloads) or
-\tcode{comp} (for the last two overloads), and
+\tcode{*this} and \tcode{x} are both sorted
+with respect to the comparator \tcode{comp}, and
 \tcode{get_allocator() == x.get_allocator()} is \tcode{true}.
 
 \pnum
 \effects
-If \tcode{addressof(x) == this}, does nothing; otherwise, merges the two sorted ranges \tcode{[begin(),
-end())} and \tcode{[x.\brk{}begin(), x.end())}. The result is a range in which the elements
-will be sorted in non-decreasing order according to the ordering defined by \tcode{comp}; that
-is, for every iterator \tcode{i}, in the range other than the first, the condition
-\tcode{comp(*i, *(i - 1))} will be \tcode{false}.
+If \tcode{addressof(x) == this}, there are no effects.
+Otherwise, merges
+the two sorted ranges \range{begin()}{end()} and \range{x.begin()}{x.end()}.
+The result is a range
+that is sorted with respect to the comparator \tcode{comp}.
 Pointers and references to the moved elements of \tcode{x} now refer to those same elements
 but as members of \tcode{*this}. Iterators referring to the moved elements will continue to
 refer to their elements, but they now behave as iterators into \tcode{*this}, not into
 \tcode{x}.
 
 \pnum
 \complexity
-At most
-\tcode{size() + x.size() - 1}
-applications of \tcode{comp} if
-\tcode{addressof(x) != this};
-otherwise, no applications of \tcode{comp} are performed.
-If an exception is thrown other than by a comparison there are no effects.
+At most \tcode{size() + x.size() - 1} comparisons
+if \tcode{addressof(x) != this};
+otherwise, no comparisons are performed.
 
 \pnum
 \remarks
-Stable\iref{algorithm.stable}. If \tcode{addressof(x) != this}, the range \tcode{[x.begin(), x.end())}
-is empty after the merge.
+Stable\iref{algorithm.stable}.
+If \tcode{addressof(x) != this}, \tcode{x} is empty after the merge.
 No elements are copied by this operation.
+If an exception is thrown other than by a comparison there are no effects.
 \end{itemdescr}
 
 \indexlibrarymember{reverse}{list}%

source/diagnostics.tex

@@ -1046,11 +1046,13 @@
 pointer to the string \tcode{"system"}. The object's \tcode{default_error_condition}
 virtual function shall behave as follows:
 
-If the argument \tcode{ev} corresponds to a POSIX \tcode{errno} value \tcode{posv}, the
-function shall return \tcode{error_condition(posv, generic_category())}.
-Otherwise, the function shall return \tcode{error_condition(ev,
-system_category())}. What constitutes correspondence for any given operating
-system is unspecified.
+If the argument \tcode{ev} is equal to 0,
+the function returns \tcode{error_condition(0, generic_category())}.
+Otherwise,
+if \tcode{ev} corresponds to a POSIX \tcode{errno} value \tcode{pxv},
+the function returns \tcode{error_condition(pxv, generic_category())}.
+Otherwise, the function returns \tcode{error_condition(ev, system_category())}.
+What constitutes correspondence for any given operating system is unspecified.
 \begin{note}
 The number of potential system error codes is large
 and unbounded, and some might not correspond to any POSIX \tcode{errno} value. Thus

source/iostreams.tex

@@ -12668,6 +12668,12 @@
   path weakly_canonical(const path& p, error_code& ec);
 }
 
+// \ref{fs.path.hash}, hash support
+namespace std {
+  template<class T> struct hash;
+  template<> struct hash<filesystem::path>;
+}
+
 namespace std::ranges {
   template<>
     inline constexpr bool enable_borrowed_range<filesystem::directory_iterator> = true;
@@ -14618,6 +14624,19 @@
 Equivalent to: \tcode{return path(lhs) /= rhs;}
 \end{itemdescr}
 
+\rSec3[fs.path.hash]{Hash support}
+
+\begin{itemdecl}
+template<> struct hash<filesystem::path>;
+\end{itemdecl}
+
+\begin{itemdescr}
+\pnum
+For an object \tcode{p} of type \tcode{filesystem::path},
+\tcode{hash<filesystem::path>()(p)} evaluates to the same result as
+\tcode{filesystem::hash_value(p)}.
+\end{itemdescr}
+
 \rSec2[fs.class.filesystem.error]{Class \tcode{filesystem_error}}
 
 \rSec3[fs.class.filesystem.error.general]{General}

source/iterators.tex

@@ -1911,8 +1911,12 @@
 The type \tcode{I} models \libconcept{contiguous_iterator} only if
 \begin{itemize}
 \item \tcode{to_address(a) == addressof(*a)},
-\item \tcode{to_address(b) == to_address(a) + D(b - a)}, and
-\item \tcode{to_address(c) == to_address(a) + D(c - a)}.
+\item \tcode{to_address(b) == to_address(a) + D(b - a)},
+\item \tcode{to_address(c) == to_address(a) + D(c - a)},
+\item \tcode{ranges::iter_move(a)} has
+the same type, value category, and effects as \tcode{std::move(*a)}, and
+\item if \tcode{ranges::iter_swap(a, b)} is well-formed,
+it has effects equivalent to \tcode{ranges::swap(*a, *b)}.
 \end{itemize}
 
 \rSec2[iterator.cpp17]{\Cpp{}17 iterator requirements}
@@ -2088,6 +2092,9 @@
 The implementation of an algorithm on input iterators
 should never attempt to pass through the same iterator twice;
 such an algorithm should be a single pass algorithm.
+
+\newpage
+
 \begin{note}
 For input iterators, \tcode{a == b} does not imply \tcode{++a == ++b}.
 (Equality does not guarantee the substitution property or referential transparency.)
@@ -2107,8 +2114,6 @@
 and the expressions in \tref{outputiterator}
 are valid and have the indicated semantics.
 
-\newpage
-
 \begin{libreqtab4b}[floattable]
 {\defnoldconcept{OutputIterator} requirements (in addition to \oldconcept{Iterator})}
 {outputiterator}
@@ -4867,9 +4872,9 @@
 otherwise it denotes \tcode{input_iterator_tag}.
 
 \item
+Let \tcode{a} denote an lvalue of type \tcode{const common_iterator<I, S>}.
 If the expression \tcode{a.operator->()} is well-formed,
-where \tcode{a} is an lvalue of type \tcode{const common_iterator<I, S>},
-then \tcode{pointer} denotes the type of that expression.
+then \tcode{pointer} denotes \tcode{decltype(a.operator->())}.
 Otherwise, \tcode{pointer} denotes \keyword{void}.
 \end{itemize}
 
@@ -5060,8 +5065,11 @@
 Otherwise, if
 \tcode{requires(I\& i) \{ \{ *i++ \} -> \exposconceptnc{can-reference}; \}}
 is \tcode{true} or
-\tcode{\libconceptx{constructible_\newline{}from}{constructible_from}<iter_value_t<I>, iter_reference_t<I>> \&\& \libconcept{move_constructible}<iter_value_t<I>>}
-is \linebreak \tcode{false},
+\begin{codeblock}
+@\libconcept{indirectly_readable}@<I> && @\libconcept{constructible_from}@<iter_value_t<I>, iter_reference_t<I>> &&
+@\libconcept{move_constructible}@<iter_value_t<I>>
+\end{codeblock}
+is \tcode{false},
 equivalent to:
 \begin{codeblock}
 return get<I>(v_)++;
@@ -5273,7 +5281,7 @@
       requires @\libconcept{contiguous_iterator}@<I>;
 
     constexpr counted_iterator& operator++();
-    decltype(auto) operator++(int);
+    constexpr decltype(auto) operator++(int);
     constexpr counted_iterator operator++(int)
       requires @\libconcept{forward_iterator}@<I>;
     constexpr counted_iterator& operator--()
@@ -5491,7 +5499,7 @@
 
 \indexlibrarymember{operator++}{counted_iterator}%
 \begin{itemdecl}
-decltype(auto) operator++(int);
+constexpr decltype(auto) operator++(int);
 \end{itemdecl}
 
 \begin{itemdescr}

source/ranges.tex

@@ -2471,7 +2471,7 @@
 \remarks
 The expression in the \grammarterm{requires-clause} is equivalent to:
 \begin{codeblock}
-(@\libconcept{same_as}@<W, Bound> && @\exposconcept{advanceable}@<W>) || (@\libconcept{integral}@<W> && @\libconcept{integral}@<Bound>) ||
+(@\libconcept{same_as}@<W, Bound> && @\exposconcept{advanceable}@<W>) || (@\exposid{is-integer-like}@<W> && @\exposid{is-integer-like}@<Bound>) ||
   @\libconcept{sized_sentinel_for}@<Bound, W>
 \end{codeblock}
 \end{itemdescr}
@@ -4125,7 +4125,8 @@
     constexpr const iterator_t<@\exposid{Base}@>& base() const & noexcept;
     constexpr iterator_t<@\exposid{Base}@> base() &&;
 
-    constexpr decltype(auto) operator*() const {
+    constexpr decltype(auto) operator*() const
+      noexcept(noexcept(invoke(*@\exposid{parent_}@->@\exposid{fun_}@, *@\exposid{current_}@))) {
       return invoke(*@\exposid{parent_}@->@\exposid{fun_}@, *@\exposid{current_}@);
     }
 
@@ -4169,14 +4170,6 @@
       requires @\libconcept{random_access_range}@<@\exposid{Base}@>;
     friend constexpr difference_type operator-(const @\exposid{iterator}@& x, const @\exposid{iterator}@& y)
       requires @\libconcept{sized_sentinel_for}@<iterator_t<@\exposid{Base}@>, iterator_t<@\exposid{Base}@>>;
-
-    friend constexpr decltype(auto) iter_move(const @\exposid{iterator}@& i)
-      noexcept(noexcept(invoke(*i.@\exposid{parent_}@->@\exposid{fun_}@, *i.@\exposid{current_}@))) {
-      if constexpr (is_lvalue_reference_v<decltype(*i)>)
-        return std::move(*i);
-      else
-        return *i;
-    }
   };
 }
 \end{codeblock}

source/strings.tex

@@ -1088,6 +1088,10 @@
 refers to the \tcode{size_type} member type of
 the type deduced by the deduction guide.
 
+\pnum
+The types \tcode{iterator} and \tcode{const_iterator} meet
+the constexpr iterator requirements\iref{iterator.requirements.general}.
+
 \rSec3[string.require]{General requirements}
 
 \pnum

source/support.tex

@@ -650,7 +650,6 @@
 #define @\defnlibxname{cpp_lib_math_constants}@                    201907L // also in \libheader{numbers}
 #define @\defnlibxname{cpp_lib_math_special_functions}@            201603L // also in \libheader{cmath}
 #define @\defnlibxname{cpp_lib_memory_resource}@                   201603L // also in \libheader{memory_resource}
-#define @\defnlibxname{cpp_lib_monadic_optional}@                  202110L // also in \libheader{optional}
 #define @\defnlibxname{cpp_lib_move_only_function}@                202110L // also in \libheader{functional}
 #define @\defnlibxname{cpp_lib_node_extract}@                      201606L
   // also in \libheader{map}, \libheader{set}, \libheader{unordered_map}, \libheader{unordered_set}
@@ -659,7 +658,7 @@
   // \libheader{unordered_map}, \libheader{unordered_set}, \libheader{vector}
 #define @\defnlibxname{cpp_lib_not_fn}@                            201603L // also in \libheader{functional}
 #define @\defnlibxname{cpp_lib_null_iterators}@                    201304L // also in \libheader{iterator}
-#define @\defnlibxname{cpp_lib_optional}@                          202106L // also in \libheader{optional}
+#define @\defnlibxname{cpp_lib_optional}@                          202110L // also in \libheader{optional}
 #define @\defnlibxname{cpp_lib_out_ptr}@                           202106L // also in \libheader{memory}
 #define @\defnlibxname{cpp_lib_parallel_algorithm}@                201603L // also in \libheader{algorithm}, \libheader{numeric}
 #define @\defnlibxname{cpp_lib_polymorphic_allocator}@             201902L // also in \libheader{memory_resource}