Merge 2024-11 LWG Motion 1

P3504R0 C++ Standard Library Ready Issues to be moved in Wrocław, Nov. 2024

Author: tkoeppe

source/algorithms.tex

@@ -11167,13 +11167,20 @@
 
 \pnum
 Some algorithms specified in \ref{specialized.algorithms}
-make use of the exposition-only function template
-\tcode{\placeholdernc{voidify}}:
+make use of the following exposition-only function templates:
 \begin{codeblock}
 template<class T>
   constexpr void* @\placeholdernc{voidify}@(T& obj) noexcept {
     return addressof(obj);
   }
+
+template<class I>
+  decltype(auto) @\exposid{deref-move}@(I& it) {
+    if constexpr (is_lvalue_reference_v<decltype(*it)>)
+      return std::move(*it);
+    else
+      return *it;
+  }
 \end{codeblock}
 
 \rSec2[special.mem.concepts]{Special memory concepts}
@@ -11550,7 +11557,7 @@
 \begin{codeblock}
 for (; first != last; (void)++result, ++first)
   ::new (@\placeholdernc{voidify}@(*result))
-    typename iterator_traits<NoThrowForwardIterator>::value_type(std::move(*first));
+    typename iterator_traits<NoThrowForwardIterator>::value_type(@\exposid{deref-move}@(first));
 return result;
 \end{codeblock}
 \end{itemdescr}
@@ -11610,7 +11617,7 @@
 \begin{codeblock}
 for (; n > 0; ++result, (void) ++first, --n)
   ::new (@\placeholdernc{voidify}@(*result))
-    typename iterator_traits<NoThrowForwardIterator>::value_type(std::move(*first));
+    typename iterator_traits<NoThrowForwardIterator>::value_type(@\exposid{deref-move}@(first));
 return {first, result};
 \end{codeblock}
 \end{itemdescr}
@@ -11741,14 +11748,22 @@
 \begin{itemdescr}
 \pnum
 \constraints
-The expression \tcode{::new (declval<void*>()) T(declval<Args>()...)}
+\tcode{is_unbounded_array_v<T>} is \tcode{false}.
+The expression \tcode{::new (declval<void*>()) T(\linebreak{}declval<Args>()...)}
 is well-formed when treated as an unevaluated operand\iref{term.unevaluated.operand}.
 
+\pnum
+\mandates
+If \tcode{is_array_v<T>} is \tcode{true}, \tcode{sizeof...(Args)} is zero.
+
 \pnum
 \effects
 Equivalent to:
 \begin{codeblock}
-return ::new (@\placeholdernc{voidify}@(*location)) T(std::forward<Args>(args)...);
+if constexpr (is_array_v<T>)
+  return ::new (@\placeholdernc{voidify}@(*location)) T[1]();
+else
+  return ::new (@\placeholdernc{voidify}@(*location)) T(std::forward<Args>(args)...);
 \end{codeblock}
 \end{itemdescr}
 
@@ -11919,7 +11934,8 @@
 \begin{itemdecl}
 template<class R, class G, class D>
   requires @\libconcept{output_range}@<R, invoke_result_t<D&, G&>> && @\libconcept{invocable}@<D&, G&> &&
-           @\libconcept{uniform_random_bit_generator}@<remove_cvref_t<G>>
+           @\libconcept{uniform_random_bit_generator}@<remove_cvref_t<G>> &&
+           is_arithmetic_v<invoke_result_t<D&, G&>>
 constexpr borrowed_iterator_t<R> ranges::generate_random(R&& r, G&& g, D&& d);
 \end{itemdecl}
 
@@ -11968,7 +11984,8 @@
 
 \begin{itemdecl}
 template<class G, class D, @\libconcept{output_iterator}@<invoke_result_t<D&, G&>> O, @\libconcept{sentinel_for}@<O> S>
-  requires @\libconcept{invocable}@<D&, G&> && @\libconcept{uniform_random_bit_generator}@<remove_cvref_t<G>>
+  requires @\libconcept{invocable}@<D&, G&> && @\libconcept{uniform_random_bit_generator}@<remove_cvref_t<G>> &&
+           is_arithmetic_v<invoke_result_t<D&, G&>>
 constexpr O ranges::generate_random(O first, S last, G&& g, D&& d);
 \end{itemdecl}
 

source/containers.tex

@@ -1463,7 +1463,7 @@
 \pnum
 \expects
 \tcode{T} is \oldconcept{EmplaceConstructible} into \tcode{X} from \tcode{args}.
-For \tcode{vector} and \tcode{deque},
+For \tcode{vector}, \tcode{inplace_vector}, and \tcode{deque},
 \tcode{T} is also \oldconcept{MoveInsertable} into \tcode{X} and
 \oldconcept{MoveAssignable}.
 
@@ -7200,10 +7200,13 @@
 \rSec3[forward.list.modifiers]{Modifiers}
 
 \pnum
-None of the overloads of \tcode{insert_after} shall affect the validity of iterators and
-references, and \tcode{erase_after} shall invalidate only iterators and references to
-the erased elements. If an exception is thrown during \tcode{insert_after} there shall
-be no effect. Inserting \tcode{n} elements into a \tcode{forward_list} is linear in
+The member functions in this subclause
+do not affect the validity of iterators and references
+when inserting elements, and when erasing elements
+invalidate iterators and references to the erased elements only.
+If an exception is thrown by any of these member functions
+there is no effect on the container.
+Inserting \tcode{n} elements into a \tcode{forward_list} is linear in
 \tcode{n}, and the number of calls to the copy or move constructor of \tcode{T} is
 exactly equal to \tcode{n}. Erasing \tcode{n} elements from a \tcode{forward_list} is
 linear in \tcode{n} and the number of calls to the destructor of type \tcode{T} is
@@ -7780,7 +7783,7 @@
 \begin{itemdescr}
 \pnum
 \effects
-Equivalent to: \tcode{return erase_if(c, [\&](auto\& elem) \{ return elem == value; \});}
+Equivalent to: \tcode{return erase_if(c, [\&](const auto\& elem) -> bool \{ return elem == value; \});}
 \end{itemdescr}
 
 \indexlibrarymember{erase_if}{forward_list}%
@@ -8564,7 +8567,7 @@
 \begin{itemdescr}
 \pnum
 \effects
-Equivalent to: \tcode{return erase_if(c, [\&](auto\& elem) \{ return elem == value; \});}
+Equivalent to: \tcode{return erase_if(c, [\&](const auto\& elem) -> bool \{ return elem == value; \});}
 \end{itemdescr}
 
 \indexlibrarymember{erase_if}{list}%
@@ -9255,8 +9258,6 @@
 
     // bit reference
     class @\libmember{reference}{vector<bool>}@ {
-      constexpr reference() noexcept;
-
     public:
       constexpr reference(const reference&) = default;
       constexpr ~reference();

source/iostreams.tex

@@ -6816,7 +6816,7 @@
 \effects
 Equivalent to:
 \begin{codeblock}
-print(os, "{}\n", format(fmt, std::forward<Args>(args)...));
+print(os, "{}\n", format(os.getloc(), fmt, std::forward<Args>(args)...));
 \end{codeblock}
 \end{itemdescr}
 
@@ -6854,25 +6854,31 @@
 without regard to the value of \tcode{os.exceptions()} and
 without turning on \tcode{ios_base::badbit} in the error state of \tcode{os}.
 \end{itemize}
+
+\par % This paragraph is part of the \effects clause.
 After constructing a \tcode{sentry} object,
 the function initializes a variable with automatic storage duration via
 \begin{codeblock}
 string out = vformat(os.getloc(), fmt, args);
 \end{codeblock}
+\begin{itemize}
+\item
 If the function is \tcode{vprint_unicode} and
-\tcode{os} is a stream that refers to a terminal capable of displaying Unicode
+\tcode{os} is a stream that refers to a terminal that
+is capable of displaying Unicode only via a native Unicode API,
 which is determined in an implementation-defined manner,
+flushes \tcode{os} and then
 writes \tcode{out} to the terminal using the native Unicode API;
 if \tcode{out} contains invalid code units,
 \indextext{undefined}%
-the behavior is undefined and
-implementations are encouraged to diagnose it.
-If the native Unicode API is used,
-the function flushes \tcode{os} before writing \tcode{out}.
-Otherwise (if \tcode{os} is not such a stream or
-the function is \tcode{vprint_nonunicode}),
+the behavior is undefined.
+\item
+Otherwise
 inserts the character sequence
 \range{out.begin()}{out.end()} into \tcode{os}.
+\end{itemize}
+
+\par % This paragraph is part of the \effects clause.
 If writing to the terminal or inserting into \tcode{os} fails,
 calls \tcode{os.setstate(ios_base::badbit)}
 (which may throw \tcode{ios_base::failure}).
@@ -7837,28 +7843,27 @@
 Let \tcode{out} denote the character representation of
 formatting arguments provided by \tcode{args}
 formatted according to specifications given in \tcode{fmt}.
-If \tcode{stream} refers to a terminal capable of displaying Unicode,
+\begin{itemize}
+\item
+If \tcode{stream} refers to a terminal that
+is capable of displaying Unicode only via a native Unicode API,
+flushes \tcode{stream} and then
 writes \tcode{out} to the terminal using the native Unicode API;
 if \tcode{out} contains invalid code units,
 \indextext{undefined}%
-the behavior is undefined and
-implementations are encouraged to diagnose it.
+the behavior is undefined.
+\item
 Otherwise writes \tcode{out} to \tcode{stream} unchanged.
-If the native Unicode API is used,
-the function flushes \tcode{stream} before writing \tcode{out}.
+\end{itemize}
 Unconditionally unlocks \tcode{stream} on function exit.
 
 \xrefc{7.21.2}.
 
 \begin{note}
-On POSIX and Windows, \tcode{stream} referring to a terminal means that,
-respectively,
-\tcode{isatty(fileno(\linebreak{}stream))} and
+On Windows the native Unicode API is \tcode{WriteConsoleW} and
+\tcode{stream} referring to a terminal means that
 \tcode{GetConsoleMode(_get_osfhandle(_fileno(stream)), ...)}
-return nonzero.
-\end{note}
-\begin{note}
-On Windows, the native Unicode API is \tcode{WriteConsoleW}.
+returns nonzero.
 \end{note}
 
 \pnum

source/iterators.tex

@@ -1969,6 +1969,7 @@
 \item \tcode{to_address(a) == addressof(*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{to_address(I\{\})} is well-defined,
 \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,

source/memory.tex

@@ -2084,6 +2084,14 @@
 }
 \end{codeblock}
 
+\pnum
+A program that instantiates the definition of \tcode{unique_ptr<T, D>}
+is ill-formed if \tcode{T*} is an invalid type.
+\begin{note}
+This prevents the intantiation of specializations such as
+\tcode{unique_ptr<T\&, D>} and \tcode{unique_ptr<int() const, D>}.
+\end{note}
+
 \pnum
 The default type for the template parameter \tcode{D} is
 \tcode{default_delete}. A client-supplied template argument
@@ -2434,9 +2442,13 @@
 \end{itemdecl}
 
 \begin{itemdescr}
+\pnum
+\mandates
+\tcode{reference_converts_from_temporary_v<add_lvalue_reference_t<T>, decltype(\linebreak{}*declval<pointer>())>} is \tcode{false}.
+
 \pnum
 \expects
-\tcode{get() != nullptr}.
+\tcode{get() != nullptr} is \tcode{true}.
 
 \pnum
 \returns
@@ -3970,15 +3982,15 @@
   \tcode{allocate_shared} shall initialize this (sub)object
   via the expression
   \begin{itemize}
-  \item \tcode{allocator_traits<A2>::construct(a2, pv, v)} or
-  \item \tcode{allocator_traits<A2>::construct(a2, pv, l...)}
+  \item \tcode{allocator_traits<A2>::construct(a2, pu, v)} or
+  \item \tcode{allocator_traits<A2>::construct(a2, pu, l...)}
   \end{itemize}
   respectively,
-  where \tcode{pv} points to storage
-  suitable to hold an object of type \tcode{U} and
-  \tcode{a2} of type \tcode{A2} is a rebound copy of
-  the allocator \tcode{a} passed to \tcode{allocate_shared}
-  such that its \tcode{value_type} is \tcode{remove_cv_t<U>}.
+  where \tcode{pu} is a pointer of type \tcode{remove_cv_t<U>*}
+  pointing to storage
+  suitable to hold an object of type \tcode{remove_cv_t<U>} and
+  \tcode{a2} of type \tcode{A2} is a potentially rebound copy of
+  the allocator \tcode{a} passed to \tcode{allocate_shared}.
 \item
   When a (sub)object of non-array type \tcode{U} is specified to have
   a default initial value,
@@ -3989,13 +4001,13 @@
 \item
   When a (sub)object of non-array type \tcode{U} is specified to have
   a default initial value,
-  \tcode{allocate_shared} shall initialize this (sub)object
-  via the expression \tcode{allocator_traits<A2>::construct(a2, pv)},
-  where \tcode{pv} points to storage
-  suitable to hold an object of type \tcode{U} and
-  \tcode{a2} of type \tcode{A2} is a rebound copy of
-  the allocator \tcode{a} passed to \tcode{allocate_shared}
-  such that its \tcode{value_type} is \tcode{remove_cv_t<U>}.
+  \tcode{allocate_shared} initializes this (sub)object
+  via the expression \tcode{allocator_traits<A2>::construct(a2, pu)},
+  where \tcode{pu} is a pointer of type \tcode{remove_cv_t<U>*}
+  pointing to storage
+  suitable to hold an object of type \tcode{remove_cv_t<U>} and
+  \tcode{a2} of type \tcode{A2} is a potentially rebound copy of
+  the allocator \tcode{a} passed to \tcode{allocate_shared}.
 \item
   When a (sub)object of non-array type \tcode{U} is initialized by
   \tcode{make_shared_for_overwrite} or\linebreak % avoid Overfull
@@ -4012,18 +4024,20 @@
   of their original construction.
 \item
   When a (sub)object of non-array type \tcode{U}
-  that was initialized by \tcode{make_shared} is to be destroyed,
-  it is destroyed via the expression \tcode{pv->\~{}U()} where
-  \tcode{pv} points to that object of type \tcode{U}.
+  that was initialized by \tcode{make_shared},
+  \tcode{make_shared_for_overwrite}, or \tcode{allocate_shared_for_overwrite}
+  is to be destroyed,
+  it is destroyed via the expression \tcode{pu->\~{}U()} where
+  \tcode{pu} points to that object of type \tcode{U}.
 \item
   When a (sub)object of non-array type \tcode{U}
   that was initialized by \tcode{allocate_shared} is to be destroyed,
   it is destroyed via the expression
-  \tcode{allocator_traits<A2>::destroy(a2, pv)} where
-  \tcode{pv} points to that object of type \tcode{remove_cv_t<U>} and
-  \tcode{a2} of type \tcode{A2} is a rebound copy of
-  the allocator \tcode{a} passed to \tcode{allocate_shared}
-  such that its \tcode{value_type} is \tcode{remove_cv_t<U>}.
+  \tcode{allocator_traits<A2>::destroy(a2, pu)} where
+  \tcode{pu} is a pointer of type \tcode{remove_cv_t<U>*}
+  pointing to that object of type \tcode{remove_cv_t<U>} and
+  \tcode{a2} of type \tcode{A2} is a potentially rebound copy of
+  the allocator \tcode{a} passed to \tcode{allocate_shared}.
 \end{itemize}
 \begin{note}
 These functions will typically allocate more memory than \tcode{sizeof(T)} to

source/meta.tex

@@ -1217,8 +1217,8 @@
   For an array type \tcode{T}, the same result as
   \tcode{has_unique_object_representations_v<remove_all_extents_t<T>>},
   otherwise \seebelow. &
-  \tcode{T} shall be a complete type, \cv{}~\keyword{void}, or
-  an array of unknown bound. \\ \rowsep
+  \tcode{remove_all_extents_t<T>} shall be a complete type or
+  \cv{}~\keyword{void}.  \\ \rowsep
 
 \indexlibraryglobal{reference_constructs_from_temporary}%
 \tcode{template<class T, class U>}\br