Merge 2025-11 LWG Motion 1

P3905R0 C++ Standard Library Ready Issues to be moved in Kona, Nov. 2025

Author: tkoeppe

source/algorithms.tex

@@ -2355,7 +2355,8 @@
 
     template<@\exposconcept{execution-policy}@ Ep, @\libconcept{random_access_iterator}@ I, @\libconcept{sized_sentinel_for}@<I> S,
              class Proj = identity, class T = projected_value_t<I, Proj>>
-      requires @\libconcept{indirect_binary_predicate}@<ranges::equal_to, projected<I, Proj>, const T*>
+      requires @\libconcept{permutable}@<I> &&
+               @\libconcept{indirect_binary_predicate}@<ranges::equal_to, projected<I, Proj>, const T*>
       subrange<I> remove(Ep&& exec, I first, S last, const T& value,
                          Proj proj = {});                                   // freestanding-deleted
     template<@\exposconcept{execution-policy}@ Ep, @\exposconcept{sized-random-access-range}@ R, class Proj = identity,
@@ -2377,6 +2378,7 @@
 
     template<@\exposconcept{execution-policy}@ Ep, @\libconcept{random_access_iterator}@ I, @\libconcept{sized_sentinel_for}@<I> S,
              class Proj = identity, @\libconcept{indirect_unary_predicate}@<projected<I, Proj>> Pred>
+      requires @\libconcept{permutable}@<I>
       subrange<I>
         remove_if(Ep&& exec, I first, S last, Pred pred, Proj proj = {});   // freestanding-deleted
     template<@\exposconcept{execution-policy}@ Ep, @\exposconcept{sized-random-access-range}@ R, class Proj = identity,
@@ -3217,6 +3219,7 @@
 
     template<@\exposconcept{execution-policy}@ Ep, @\libconcept{random_access_iterator}@ I, @\libconcept{sized_sentinel_for}@<I> S,
              class Proj = identity, @\libconcept{indirect_unary_predicate}@<projected<I, Proj>> Pred>
+      requires @\libconcept{permutable}@<I>
       subrange<I>
         partition(Ep&& exec, I first, S last, Pred pred, Proj proj = {});   // freestanding-deleted
     template<@\exposconcept{execution-policy}@ Ep, @\exposconcept{sized-random-access-range}@ R, class Proj = identity,
@@ -7561,7 +7564,8 @@
 
 template<@\exposconcept{execution-policy}@ Ep, @\libconcept{random_access_iterator}@ I, @\libconcept{sized_sentinel_for}@<I> S,
          class Proj = identity, class T = projected_value_t<I, Proj>>
-  requires @\libconcept{indirect_binary_predicate}@<ranges::equal_to, projected<I, Proj>, const T*>
+  requires @\libconcept{permutable}@<I> &&
+           @\libconcept{indirect_binary_predicate}@<ranges::equal_to, projected<I, Proj>, const T*>
   subrange<I>
     ranges::remove(Ep&& exec, I first, S last, const T& value, Proj proj = {});
 template<@\exposconcept{execution-policy}@ Ep, @\exposconcept{sized-random-access-range}@ R, class Proj = identity,
@@ -7583,6 +7587,7 @@
 
 template<@\exposconcept{execution-policy}@ Ep, @\libconcept{random_access_iterator}@ I, @\libconcept{sized_sentinel_for}@<I> S,
          class Proj = identity, @\libconcept{indirect_unary_predicate}@<projected<I, Proj>> Pred>
+  requires @\libconcept{permutable}@<I>
   subrange<I>
     ranges::remove_if(Ep&& exec, I first, S last, Pred pred, Proj proj = {});
 template<@\exposconcept{execution-policy}@ Ep, @\exposconcept{sized-random-access-range}@ R, class Proj = identity,
@@ -7943,10 +7948,10 @@
 \begin{itemize}
 \setlength{\emergencystretch}{1em}
 \item
-  \tcode{bool(pred(*i, *(i - 1)))}
+  \tcode{bool(pred(*(i - 1), *i))}
   for the overloads in namespace \tcode{std};
 \item
-  \tcode{bool(invoke(comp, invoke(proj, *i), invoke(proj, *(i - 1))))}
+  \tcode{bool(invoke(comp, invoke(proj, *(i - 1)), invoke(proj, *i)))}
   for the overloads in namespace \tcode{ranges}.
 \end{itemize}
 
@@ -9696,6 +9701,7 @@
 
 template<@\exposconcept{execution-policy}@ Ep, @\libconcept{random_access_iterator}@ I, @\libconcept{sized_sentinel_for}@<I> S,
          class Proj = identity, @\libconcept{indirect_unary_predicate}@<projected<I, Proj>> Pred>
+  requires @\libconcept{permutable}@<I>
   subrange<I> ranges::partition(Ep&& exec, I first, S last, Pred pred, Proj proj = {});
 template<@\exposconcept{execution-policy}@ Ep, @\exposconcept{sized-random-access-range}@ R, class Proj = identity,
          @\libconcept{indirect_unary_predicate}@<projected<iterator_t<R>, Proj>> Pred>
@@ -13343,7 +13349,7 @@
 \begin{itemdescr}
 \pnum
 \constraints
-\tcode{T} is an arithmetic type other than \tcode{bool}.
+\tcode{T} is an arithmetic type other than \cv{}~\tcode{bool}.
 
 \pnum
 \returns

source/containers.tex

@@ -6336,10 +6336,6 @@
 In the case that \tcode{N == 0}, \tcode{begin() == end() ==} unique value.
 The return value of \tcode{data()} is unspecified.
 
-\pnum
-The effect of calling \tcode{front()} or \tcode{back()} for a zero-sized array is
-undefined.
-
 \pnum
 Member function \tcode{swap()} shall have a
 non-throwing exception specification.
@@ -8976,7 +8972,7 @@
 Equivalent to:
 \begin{codeblock}
 auto original_size = c.size();
-for (auto i = c.begin(), last = c.end(); i != last; ) {
+for (auto i = c.begin(); i != c.end(); ) {
   if (pred(*i)) {
     i = c.erase(i);
   } else {
@@ -11573,7 +11569,7 @@
                     const Allocator& = Allocator());
     constexpr map(const map& x);
     constexpr map(map&& x);
-    explicit map(const Allocator&);
+    constexpr explicit map(const Allocator&);
     constexpr map(const map&, const type_identity_t<Allocator>&);
     constexpr map(map&&, const type_identity_t<Allocator>&);
     constexpr map(initializer_list<value_type>, const Compare& = Compare(),
@@ -13450,7 +13446,8 @@
 is additional semantic information.
 
 \pnum
-The types \tcode{iterator} and \tcode{const_iterator} meet
+The types \tcode{iterator}, \tcode{const_iterator},
+\tcode{local_iterator}, and \tcode{const_local_iterator} meet
 the constexpr iterator requirements\iref{iterator.requirements.general}.
 
 \indexlibraryglobal{unordered_map}%
@@ -14245,7 +14242,8 @@
 there is additional semantic information.
 
 \pnum
-The types \tcode{iterator} and \tcode{const_iterator} meet
+The types \tcode{iterator}, \tcode{const_iterator},
+\tcode{local_iterator}, and \tcode{const_local_iterator} meet
 the constexpr iterator requirements\iref{iterator.requirements.general}.
 
 \indexlibraryglobal{unordered_multimap}%
@@ -14735,7 +14733,8 @@
 is additional semantic information.
 
 \pnum
-The types \tcode{iterator} and \tcode{const_iterator} meet
+The types \tcode{iterator}, \tcode{const_iterator},
+\tcode{local_iterator}, and \tcode{const_local_iterator} meet
 the constexpr iterator requirements\iref{iterator.requirements.general}.
 
 \indexlibraryglobal{unordered_set}%
@@ -15155,7 +15154,8 @@
 is additional semantic information.
 
 \pnum
-The types \tcode{iterator} and \tcode{const_iterator} meet
+The types \tcode{iterator}, \tcode{const_iterator},
+\tcode{local_iterator}, and \tcode{const_local_iterator} meet
 the constexpr iterator requirements\iref{iterator.requirements.general}.
 
 \indexlibraryglobal{unordered_multiset}%
@@ -15628,6 +15628,9 @@
   template<class charT, class T, @\libconcept{formattable}@<charT> Container>
     struct formatter<queue<T, Container>, charT>;
 
+  template<class T, class Container>
+    constexpr bool enable_nonlocking_formatter_optimization<queue<T, Container>> = false;
+
   // \ref{priority.queue}, class template \tcode{priority_queue}
   template<class T, class Container = vector<T>,
            class Compare = less<typename Container::value_type>>
@@ -15642,6 +15645,10 @@
   // \ref{container.adaptors.format}, formatter specialization for \tcode{priority_queue}
   template<class charT, class T, @\libconcept{formattable}@<charT> Container, class Compare>
     struct formatter<priority_queue<T, Container, Compare>, charT>;
+
+  template<class T, class Container, class Compare>
+    constexpr bool
+      enable_nonlocking_formatter_optimization<priority_queue<T, Container, Compare>> = false;
 }
 \end{codeblock}
 
@@ -16553,6 +16560,9 @@
   // \ref{container.adaptors.format}, formatter specialization for \tcode{stack}
   template<class charT, class T, @\libconcept{formattable}@<charT> Container>
     struct formatter<stack<T, Container>, charT>;
+
+  template<class T, class Container>
+    constexpr bool enable_nonlocking_formatter_optimization<stack<T, Container>> = false;
 }
 \end{codeblock}
 
@@ -19041,7 +19051,7 @@
     constexpr container_type extract() &&;
     constexpr void replace(container_type&&);
 
-    constexpr iterator erase(iterator position);
+    constexpr iterator erase(iterator position) requires (!@\libconcept{same_as}@<iterator, const_iterator>);
     constexpr iterator erase(const_iterator position);
     constexpr size_type erase(const key_type& x);
     template<class K> constexpr size_type erase(K&& x);
@@ -19712,7 +19722,7 @@
     constexpr container_type extract() &&;
     constexpr void replace(container_type&&);
 
-    constexpr iterator erase(iterator position);
+    constexpr iterator erase(iterator position) requires (!@\libconcept{same_as}@<iterator, const_iterator>);
     constexpr iterator erase(const_iterator position);
     constexpr size_type erase(const key_type& x);
     template<class K> constexpr size_type erase(K&& x);
@@ -20161,6 +20171,10 @@
 The header \libheaderref{mdspan} defines the class template \tcode{mdspan} and
 other facilities for interacting with these multidimensional views.
 
+\pnum
+In addition to being available via inclusion of the \libheaderref{span} header,
+\tcode{dynamic_extent} is available when the header \libheaderref{mdspan} is included.
+
 \rSec2[views.contiguous]{Contiguous access}
 
 \rSec3[span.syn]{Header \tcode{<span>} synopsis}%
@@ -20177,7 +20191,7 @@
   template<class T>
     concept @\defexposconcept{integral-constant-like}@ =                    // \expos
       is_integral_v<remove_cvref_t<decltype(T::value)>> &&
-      !is_same_v<bool, remove_const_t<decltype(T::value)>> &&
+      !is_same_v<bool, remove_cvref_t<decltype(T::value)>> &&
       @\libconcept{convertible_to}@<T, decltype(T::value)> &&
       @\libconcept{equality_comparable_with}@<T, decltype(T::value)> &&
       bool_constant<T() == T::value>::value &&
@@ -20644,7 +20658,7 @@
 
 \pnum
 \effects
-Equivalent to: \tcode{return R\{data(), Count\};}
+Equivalent to: \tcode{return R(data(), Count);}
 where \tcode{R} is the return type.
 \end{itemdescr}
 
@@ -20664,7 +20678,7 @@
 
 \pnum
 \effects
-Equivalent to: \tcode{return R\{data() + (size() - Count), Count\};}
+Equivalent to: \tcode{return R(data() + (size() - Count), Count);}
 where \tcode{R} is the return type.
 \end{itemdescr}
 
@@ -20719,7 +20733,8 @@
 
 \pnum
 \effects
-Equivalent to: \tcode{return \{data(), count\};}
+Equivalent to: \tcode{return R(data(), count);}
+where \tcode{R} is the return type.
 \end{itemdescr}
 
 \indexlibrarymember{span}{last}%
@@ -20734,7 +20749,8 @@
 
 \pnum
 \effects
-Equivalent to: \tcode{return \{data() + (size() - count), count\};}
+Equivalent to: \tcode{return R(data() + (size() - count), count);}
+where \tcode{R} is the return type.
 \end{itemdescr}
 
 \indexlibrarymember{span}{subspan}%
@@ -20755,8 +20771,9 @@
 \effects
 Equivalent to:
 \begin{codeblock}
-return {data() + offset, count == dynamic_extent ? size() - offset : count};
+return R(data() + offset, count == dynamic_extent ? size() - offset : count);
 \end{codeblock}
+where \tcode{R} is the return type.
 \end{itemdescr}
 
 \rSec4[span.obs]{Observers}
@@ -20959,6 +20976,10 @@
 \end{itemdecl}
 
 \begin{itemdescr}
+\pnum
+\constraints
+\tcode{is_volatile_v<ElementType>} is \tcode{false}.
+
 \pnum
 \effects
 Equivalent to: \tcode{return R\{reinterpret_cast<const byte*>(s.data()), s.size_bytes()\};}
@@ -20975,7 +20996,8 @@
 \begin{itemdescr}
 \pnum
 \constraints
-\tcode{is_const_v<ElementType>} is \tcode{false}.
+\tcode{is_const_v<ElementType>} is \tcode{false} and
+\tcode{is_volatile_v<ElementType>} is \tcode{false}.
 
 \pnum
 \effects
@@ -21246,7 +21268,7 @@
 \effects
 \begin{itemize}
 \item
-If \tcode{OtherIndexType} is an integral type other than \tcode{bool},
+If \tcode{remove_cvref_t<OtherIndexType>} is an integral type other than \tcode{bool},
 then equivalent to \tcode{return i;},
 \item
 otherwise, equivalent to \tcode{return static_cast<index_type>(i);}.
@@ -22600,7 +22622,7 @@
       constexpr index_type operator()(Indices...) const noexcept;
 
     static constexpr bool is_always_unique() noexcept { return true; }
-    static constexpr bool is_always_exhaustive() noexcept { return false; }
+    static constexpr bool is_always_exhaustive() noexcept;
     static constexpr bool is_always_strided() noexcept { return true; }
 
     static constexpr bool is_unique() noexcept { return true; }
@@ -22883,6 +22905,20 @@
 \end{codeblock}
 \end{itemdescr}
 
+\indexlibrarymember{is_always_exhaustive}{layout_stride::mapping}%
+\begin{itemdecl}
+static constexpr bool is_always_exhaustive() noexcept;
+\end{itemdecl}
+
+\begin{itemdescr}
+\pnum
+\returns
+\tcode{true} if \exposid{rank_} is 0
+or if there is a rank index \tcode{r} of \tcode{extents()}
+such that \tcode{extents_type::sta\-tic_extent(r)} is 0,
+otherwise \tcode{false}.
+\end{itemdescr}
+
 \indexlibrarymember{is_exhaustive}{layout_stride::mapping}%
 \begin{itemdecl}
 constexpr bool is_exhaustive() const noexcept;
@@ -22893,7 +22929,8 @@
 \returns
 \begin{itemize}
 \item
-\tcode{true} if \exposid{rank_} is 0.
+\tcode{true} if \exposid{rank_} or the size of the multidimensional index space
+\tcode{m.extents()} is 0.
 \item
 Otherwise, \tcode{true} if there is
 a permutation $P$ of the integers in the range $[0, \exposid{rank_})$
@@ -23058,6 +23095,7 @@
 then the size of the multidimensional index space \tcode{Extents()}
 is representable as a value of type \tcode{index_type}.
 \item
+If \tcode{padding_value} is not equal to \tcode{dynamic_extent}, then
 \tcode{padding_value} is representable as a value of type \tcode{index_type}.
 \item
 If
@@ -23684,6 +23722,7 @@
 then the size of the multidimensional index space \tcode{Extents()}
 is representable as a value of type \tcode{index_type}.
 \item
+If \tcode{padding_value} is not equal to \tcode{dynamic_extent}, then
 \tcode{padding_value} is representable as a value of type \tcode{index_type}.
 \item
 If