Merge 2026-03 LWG Motion 1

P4145R0 C++ Standard Library Ready Issues to be moved in Croydon, Mar. 2026

Author: tkoeppe

source/algorithms.tex

@@ -2316,16 +2316,6 @@
     template<@\libconcept{input_or_output_iterator}@ O, @\libconcept{copy_constructible}@ F>
       requires @\libconcept{invocable}@<F&> && @\libconcept{indirectly_writable}@<O, invoke_result_t<F&>>
       constexpr O generate_n(O first, iter_difference_t<O> n, F gen);
-    template<@\exposconcept{execution-policy}@ Ep, @\libconcept{random_access_iterator}@ O, @\libconcept{sized_sentinel_for}@<O> S,
-             @\libconcept{copy_constructible}@ F>
-      requires @\libconcept{invocable}@<F&> && @\libconcept{indirectly_writable}@<O, invoke_result_t<F&>>
-      O generate(Ep&& exec, O first, S last, F gen);                        // freestanding-deleted
-    template<@\exposconcept{execution-policy}@ Ep, @\exposconcept{sized-random-access-range}@ R, @\libconcept{copy_constructible}@ F>
-      requires @\libconcept{invocable}@<F&> && @\libconcept{indirectly_writable}@<iterator_t<R>, invoke_result_t<F&>>
-      borrowed_iterator_t<R> generate(Ep&& exec, R&& r, F gen);             // freestanding-deleted
-    template<@\exposconcept{execution-policy}@ Ep, @\libconcept{random_access_iterator}@ O, @\libconcept{copy_constructible}@ F>
-      requires @\libconcept{invocable}@<F&> && @\libconcept{indirectly_writable}@<O, invoke_result_t<F&>>
-      O generate_n(Ep&& exec, O first, iter_difference_t<O> n, F gen);      // freestanding-deleted
   }
 
   // \ref{alg.remove}, remove
@@ -2857,12 +2847,12 @@
              class Comp = ranges::less, class Proj = identity>
       requires @\libconcept{sortable}@<I, Comp, Proj>
       I stable_sort(Ep&& exec, I first, S last, Comp comp = {},
-                    Proj proj = {});                                        // freestanding-deleted
+                    Proj proj = {});                                        // hosted
     template<@\exposconcept{execution-policy}@ Ep, @\exposconcept{sized-random-access-range}@ R, class Comp = ranges::less,
              class Proj = identity>
       requires @\libconcept{sortable}@<iterator_t<R>, Comp, Proj>
       borrowed_iterator_t<R>
-        stable_sort(Ep&& exec, R&& r, Comp comp = {}, Proj proj = {});      // freestanding-deleted
+        stable_sort(Ep&& exec, R&& r, Comp comp = {}, Proj proj = {});      // hosted
   }
 
   template<class RandomAccessIterator>
@@ -3261,12 +3251,12 @@
       requires @\libconcept{permutable}@<I>
       subrange<I>
         stable_partition(Ep&& exec, I first, S last, Pred pred,
-                         Proj proj = {});                                   // freestanding-deleted
+                         Proj proj = {});                                   // hosted
     template<@\exposconcept{execution-policy}@ Ep, @\exposconcept{sized-random-access-range}@ R, class Proj = identity,
              @\libconcept{indirect_unary_predicate}@<projected<iterator_t<R>, Proj>> Pred>
       requires @\libconcept{permutable}@<iterator_t<R>>
       borrowed_subrange_t<R>
-        stable_partition(Ep&& exec, R&& r, Pred pred, Proj proj = {});      // freestanding-deleted
+        stable_partition(Ep&& exec, R&& r, Pred pred, Proj proj = {});      // hosted
   }
 
   template<class InputIterator, class OutputIterator1,
@@ -3434,13 +3424,13 @@
              class Comp = ranges::less, class Proj = identity>
       requires @\libconcept{sortable}@<I, Comp, Proj>
       I inplace_merge(Ep&& exec, I first, I middle, S last, Comp comp = {},
-                      Proj proj = {});                          // freestanding-deleted
+                      Proj proj = {});                          // hosted
     template<@\exposconcept{execution-policy}@ Ep, @\exposconcept{sized-random-access-range}@ R, class Comp = ranges::less,
              class Proj = identity>
       requires @\libconcept{sortable}@<iterator_t<R>, Comp, Proj>
       borrowed_iterator_t<R>
         inplace_merge(Ep&& exec, R&& r, iterator_t<R> middle, Comp comp = {},
-                      Proj proj = {});                          // freestanding-deleted
+                      Proj proj = {});                          // hosted
   }
 
   // \ref{alg.set.operations}, set operations
@@ -7492,17 +7482,6 @@
 template<@\libconcept{input_or_output_iterator}@ O, @\libconcept{copy_constructible}@ F>
   requires @\libconcept{invocable}@<F&> && @\libconcept{indirectly_writable}@<O, invoke_result_t<F&>>
   constexpr O ranges::generate_n(O first, iter_difference_t<O> n, F gen);
-
-template<@\exposconcept{execution-policy}@ Ep, @\libconcept{random_access_iterator}@ O, @\libconcept{sized_sentinel_for}@<O> S,
-         @\libconcept{copy_constructible}@ F>
-  requires @\libconcept{invocable}@<F&> && @\libconcept{indirectly_writable}@<O, invoke_result_t<F&>>
-  O ranges::generate(Ep&& exec, O first, S last, F gen);
-template<@\exposconcept{execution-policy}@ Ep, @\exposconcept{sized-random-access-range}@ R, @\libconcept{copy_constructible}@ F>
-  requires @\libconcept{invocable}@<F&> && @\libconcept{indirectly_writable}@<iterator_t<R>, invoke_result_t<F&>>
-  borrowed_iterator_t<R> ranges::generate(Ep&& exec, R&& r, F gen);
-template<@\exposconcept{execution-policy}@ Ep, @\libconcept{random_access_iterator}@ O, @\libconcept{copy_constructible}@ F>
-  requires @\libconcept{invocable}@<F&> && @\libconcept{indirectly_writable}@<O, invoke_result_t<F&>>
-  O ranges::generate_n(Ep&& exec, O first, iter_difference_t<O> n, F gen);
 \end{itemdecl}
 
 \begin{itemdescr}

source/containers.tex

@@ -8847,7 +8847,8 @@
 \pnum
 \throws
 \tcode{length_error} if any of \tcode{x}'s active blocks
-are not within the bounds of \exposid{current-limits}.
+are not within the bounds of \exposid{current-limits},
+as well as any exceptions thrown by the allocator.
 
 \pnum
 \complexity
@@ -10651,6 +10652,18 @@
 \tcode{*this}.
 \end{itemdescr}
 
+\indexlibrarymember{operator bool}{vector<bool>::reference}%
+\begin{itemdecl}
+constexpr reference::operator bool() const noexcept;
+\end{itemdecl}
+
+\begin{itemdescr}
+\pnum
+\returns
+\tcode{true} if the value of the bit referred to by \tcode{*this} is one,
+\tcode{false} otherwise.
+\end{itemdescr}
+
 \indexlibrarymember{flip}{vector<bool>::reference}%
 \begin{itemdecl}
 constexpr void reference::flip() noexcept;
@@ -19494,8 +19507,8 @@
 \effects
 Adds elements to \exposid{c} as if by:
 \begin{codeblock}
-ranges::for_each(rg, [&](auto&& e) {
-  @\exposid{c}@.insert(@\exposid{c}@.end(), std::forward<decltype(e)>(e));
+ranges::for_each(rg, [&](value_type e) {
+  @\exposid{c}@.insert(@\exposid{c}@.end(), std::move(e));
 });
 \end{codeblock}
 Then,
@@ -20182,8 +20195,8 @@
 \effects
 Adds elements to \exposid{c} as if by:
 \begin{codeblock}
-ranges::for_each(rg, [&](auto&& e) {
-  @\exposid{c}@.insert(@\exposid{c}@.end(), std::forward<decltype(e)>(e));
+ranges::for_each(rg, [&](value_type e) {
+  @\exposid{c}@.insert(@\exposid{c}@.end(), std::move(e));
 });
 \end{codeblock}
 Then, sorts the range of newly inserted elements with respect to \exposid{compare},
@@ -20392,10 +20405,7 @@
     concept @\defexposconcept{integral-constant-like}@ =                    // \expos
       is_integral_v<remove_cvref_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 &&
-      bool_constant<static_cast<decltype(T::value)>(T()) == T::value>::value;
+      @\exposconcept{constexpr-wrapper-like}@<T>;
 
   template<class T>
     constexpr size_t @\defexposconcept{maybe-static-ext}@ = dynamic_extent; // \expos
@@ -21289,12 +21299,12 @@
   inline constexpr full_extent_t full_extent{};
 
   template<class IndexType, size_t... Extents, class... SliceSpecifiers>
-    constexpr auto submdspan_extents(const extents<IndexType, Extents...>&, SliceSpecifiers...);
+    constexpr auto subextents(const extents<IndexType, Extents...>&, SliceSpecifiers...);
 
   // \ref{mdspan.sub.canonical}, \tcode{submdspan} slice canonicalization
   template<class IndexType, size_t... Extents, class... Slices>
-    constexpr auto submdspan_canonicalize_slices(const extents<IndexType, Extents...>& src,
-                                                 Slices... slices);
+    constexpr auto canonical_slices(const extents<IndexType, Extents...>& src,
+                                    Slices... slices);
 
   // \ref{mdspan.sub.sub}, \tcode{submdspan} function template
   template<class ElementType, class Extents, class LayoutPolicy,
@@ -25033,7 +25043,7 @@
                 typename MappingType::layout_type>;
 
   template<class MappingType, class AccessorType>
-    mdspan(const typename AccessorType::data_handle_type&, const MappingType&,
+    mdspan(typename AccessorType::data_handle_type, const MappingType&,
            const AccessorType&)
       -> mdspan<typename AccessorType::element_type, typename MappingType::extents_type,
                 typename MappingType::layout_type, AccessorType>;
@@ -25846,11 +25856,12 @@
 
 \rSec4[mdspan.sub.canonical]{\tcode{submdspan} slice canonicalization}
 
-\indexlibraryglobal{submdspan_canonicalize_slices}%
+%FIXME: "Slices" is used instead of "SliceSpecifiers" in the synopsis declaration.
+\indexlibraryglobal{canonical_slices}%
 \begin{itemdecl}
 template<class IndexType, size_t... Extents, class... SliceSpecifiers>
-  constexpr auto submdspan_canonicalize_slices(const extents<IndexType, Extents...>& src,
-                                               SliceSpecifiers... slices);
+  constexpr auto canonical_slices(const extents<IndexType, Extents...>& src,
+                                  SliceSpecifiers... slices);
 \end{itemdecl}
 
 \begin{itemdescr}
@@ -25882,20 +25893,20 @@
 \tcode{make_tuple(\exposid{canonical-slice}<IndexType>(slices)...)}.
 \end{itemdescr}
 
-\rSec4[mdspan.sub.extents]{\tcode{submdspan_extents} function}
+\rSec4[mdspan.sub.extents]{\tcode{subextents} function}
 
-\indexlibraryglobal{submdspan_extents}%
+\indexlibraryglobal{subextents}%
 \begin{itemdecl}
 template<class IndexType, size_t... Extents, class... SliceSpecifiers>
-  constexpr auto submdspan_extents(const extents<IndexType, Extents...>& src,
-                                   SliceSpecifiers... raw_slices);
+  constexpr auto subextents(const extents<IndexType, Extents...>& src,
+                            SliceSpecifiers... raw_slices);
 \end{itemdecl}
 
 \begin{itemdescr}
 \pnum
 Let \tcode{slices} be the pack introduced by the following declaration:
 \begin{codeblock}
-auto [...slices] = submdspan_canonicalize_slices(src, raw_slices...);
+auto [...slices] = canonical_slices(src, raw_slices...);
 \end{codeblock}
 
 \pnum
@@ -26048,7 +26059,7 @@
 An object \tcode{smr} of type \tcode{SMR} such that
 \begin{itemize}
 \item
-  \tcode{smr.mapping.extents() == submdspan_extents(m.extents(), valid_slices...)}
+  \tcode{smr.mapping.extents() == subextents(m.extents(), valid_slices...)}
   is \tcode{true};\newline and
 \item
   for each integer pack \tcode{i}
@@ -26121,7 +26132,7 @@
 
 \pnum
 Let \tcode{sub_ext} be
-the result of \tcode{submdspan_extents(extents(), slices...)} and
+the result of \tcode{subextents(extents(), slices...)} and
 let \tcode{SubExtents} be \tcode{decl\-type(sub_ext)}.
 
 \pnum
@@ -26502,7 +26513,7 @@
 \pnum
 Let \tcode{slices} be the pack introduced by the following declaration:
 \begin{codeblock}
-auto [...slices] = submdspan_canonicalize_slices(src, raw_slices...);
+auto [...slices] = canonical_slices(src, raw_slices...);
 \end{codeblock}
 
 \pnum

source/diagnostics.tex

@@ -495,8 +495,11 @@
 
 \pnum
 If \mname{VA_ARGS} does not expand to
-an \grammarterm{assignment-expression},
+a  well-formed \grammarterm{assignment-expression},
 the program is ill-formed.
+If such an \grammarterm{assignment-expression} is ill-formed when
+treated as an unevaluated operand\iref{expr.await, expr.yield},
+the program is ill-formed, no diagnostic required.
 
 \pnum
 The macro \tcode{assert} is redefined according to

source/exec.tex

@@ -7227,7 +7227,6 @@
 
   public:
     using sender_concept = sender_t;
-    using completion_signatures = @\seebelow@;
     using allocator_type = @\seebelow@;
     using scheduler_type = @\seebelow@;
     using stop_source_type = @\seebelow@;
@@ -7240,6 +7239,9 @@
     task(task&&) noexcept;
     ~task();
 
+    template<class Self, class... Env>
+      static consteval auto get_completion_signatures();
+
     template<@\libconcept{receiver}@ Rcvr>
       @\exposid{state}@<Rcvr> connect(Rcvr&& rcvr) &&;
 
@@ -7281,19 +7283,6 @@
 contain an element which is not of the form
 \tcode{set_error_t(E)} for some type \tcode{E}.
 
-\pnum
-The type alias \tcode{completion_signatures} is a specialization
-of \tcode{execution::completion_signatures} with the template
-arguments (in unspecified order):
-\begin{itemize}
-\item \tcode{set_value_t()} if \tcode{T} is \tcode{void},
-and \tcode{set_value_t(T)} otherwise;
-\item template arguments of the specialization of
-\tcode{execution::completion_signatures} denoted by \tcode{error_types};
-and
-\item \tcode{set_stopped_t()}.
-\end{itemize}
-
 \pnum
 \tcode{allocator_type} shall meet the \oldconcept{Allocator}
 requirements.
@@ -7325,6 +7314,32 @@
 \end{codeblock}
 \end{itemdescr}
 
+\indexlibrarymember{get_completion_signatures}{task}%
+\begin{itemdecl}
+template<class Self, class... Env>
+  static consteval auto get_completion_signatures();
+\end{itemdecl}
+\begin{itemdescr}
+\pnum
+Let the type \tcode{C} be a specialization
+of \tcode{execution::completion_signatures}
+with the template arguments (in unspecified order):
+\begin{itemize}
+\item
+\tcode{set_value_t()} if \tcode{T} is \tcode{void},
+and \tcode{set_value_t(T)} otherwise;
+\item
+template arguments of the specialization of
+\tcode{execution::completion_signatures} denoted by \tcode{error_types};
+and
+\item \tcode{set_stopped_t()}.
+\end{itemize}
+
+\pnum
+\returns
+\tcode{C()}.
+\end{itemdescr}
+
 \indexlibrarymember{connect}{task}%
 \begin{itemdecl}
 template<@\libconcept{receiver}@ Rcvr>
@@ -7476,8 +7491,8 @@
     template<class E>
       @\unspec@ yield_value(with_error<E> error);
 
-    template<class A>
-      auto await_transform(A&& a);
+    template<@\libconcept{sender}@ Sender>
+      auto await_transform(Sender&& sndr);
     template<class Sch>
       auto await_transform(change_coroutine_scheduler<Sch> sch);
 
@@ -7568,7 +7583,7 @@
 \tcode{set_value(std::move(\exposid{RCVR}(*this)))} if \tcode{is_void<T>} is \tcode{true},
 and otherwise
 \item
- \tcode{set_value(std::move(\exposid{RCVR}(*this)), *\exposid{result})}.
+ \tcode{set_value(std::move(\exposid{RCVR}(*this)), std::move(*\exposid{result}))}.
 \end{itemize}
 \end{itemdescr}
 
@@ -7596,7 +7611,7 @@
 \indexlibrarymember{await_transform}{task::promise_type}%
 \begin{itemdecl}
 template<@\libconcept{sender}@ Sender>
-  auto await_transform(Sender&& sndr) noexcept;
+  auto await_transform(Sender&& sndr);
 \end{itemdecl}
 \begin{itemdescr}
 \pnum
@@ -7610,14 +7625,14 @@
 \indexlibrarymember{await_transform}{task::promise_type}%
 \begin{itemdecl}
 template<class Sch>
-  auto await_transform(change_coroutine_scheduler<Sch> sch) noexcept;
+  auto await_transform(change_coroutine_scheduler<Sch> sch);
 \end{itemdecl}
 \begin{itemdescr}
 \pnum
 \effects
 Equivalent to:
 \begin{codeblock}
-return await_transform(just(exchange(@\exposid{SCHED}@(*this), scheduler_type(sch.scheduler))), *this);
+return as_awaitable(just(exchange(@\exposid{SCHED}@(*this), scheduler_type(sch.scheduler))), *this);
 \end{codeblock}
 \end{itemdescr}
 

source/future.tex

@@ -929,7 +929,7 @@
 \begin{itemdescr}
 \pnum
 \returns
-\tcode{system_encoded_string()}.
+\tcode{native_encoded_string()}.
 \end{itemdescr}
 
 \indexlibrarymember{generic_string}{path}%
@@ -940,7 +940,7 @@
 \begin{itemdescr}
 \pnum
 \returns
-\tcode{generic_system_encoded_string()}.
+\tcode{generic_native_encoded_string()}.
 \end{itemdescr}
 
 \rSec1[depr.atomics]{Deprecated atomic operations}