Merge 2025-11 LWG Motion 12

P3612R1 Harmonize proxy-reference operations (LWG 3638 and 4187)

Author: tkoeppe

source/containers.tex

@@ -10480,13 +10480,17 @@
     // bit reference
     class @\libmember{reference}{vector<bool>}@ {
     public:
-      constexpr reference(const reference&) = default;
+      constexpr reference(const reference& x) noexcept;
       constexpr ~reference();
-      constexpr operator bool() const noexcept;
       constexpr reference& operator=(bool x) noexcept;
       constexpr reference& operator=(const reference& x) noexcept;
       constexpr const reference& operator=(bool x) const noexcept;
+      constexpr operator bool() const noexcept;
       constexpr void flip() noexcept;   // flips the bit
+
+      friend constexpr void swap(reference x, reference y) noexcept;
+      friend constexpr void swap(reference x, bool& y) noexcept;
+      friend constexpr void swap(bool& x, reference y) noexcept;
     };
 
     // construct/copy/destroy
@@ -10572,7 +10576,6 @@
     constexpr void swap(vector&)
       noexcept(allocator_traits<Allocator>::propagate_on_container_swap::value ||
                allocator_traits<Allocator>::is_always_equal::value);
-    static constexpr void swap(reference x, reference y) noexcept;
     constexpr void flip() noexcept;     // flips all bits
     constexpr void clear() noexcept;
   };
@@ -10594,39 +10597,89 @@
 
 \pnum
 \tcode{reference}
-is a class that simulates the behavior of references of a single bit in
-\tcode{vector<bool>}. The conversion function returns \tcode{true}
-when the bit is set, and \tcode{false} otherwise. The assignment operators
-set the bit when the argument is (convertible to) \tcode{true} and
-clear it otherwise. \tcode{flip} reverses the state of the bit.
+is a class that simulates a reference to a single bit in the sequence.
 
-\indexlibrarymember{flip}{vector<bool>}%
+\indexlibraryctor{vector<bool>::reference}%
 \begin{itemdecl}
-constexpr void flip() noexcept;
+constexpr reference::reference(const reference& x) noexcept;
 \end{itemdecl}
 
 \begin{itemdescr}
 \pnum
 \effects
-Replaces each element in the container with its complement.
+Initializes \tcode{*this} to refer to the same bit as \tcode{x}.
+\end{itemdescr}
+
+\indexlibrarydtor{vector<bool>::reference}%
+\begin{itemdecl}
+constexpr reference::~reference();
+\end{itemdecl}
+
+\begin{itemdescr}
+\pnum
+\effects
+None.
 \end{itemdescr}
 
-\indexlibrarymember{swap}{vector<bool>}%
+\indexlibrarymember{operator=}{vector<bool>::reference}%
 \begin{itemdecl}
-static constexpr void swap(reference x, reference y) noexcept;
+constexpr reference& reference::operator=(bool x) noexcept;
+constexpr reference& reference::operator=(const reference& x) noexcept;
+constexpr const reference& reference::operator=(bool x) const noexcept;
 \end{itemdecl}
 
 \begin{itemdescr}
 \pnum
 \effects
-Exchanges the contents of \tcode{x} and \tcode{y} as if by:
+Sets the bit referred to by \tcode{*this} when \tcode{bool(x)} is \tcode{true},
+and clears it otherwise.
+
+\pnum
+\returns
+\tcode{*this}.
+\end{itemdescr}
+
+\indexlibrarymember{flip}{vector<bool>::reference}%
+\begin{itemdecl}
+constexpr void reference::flip() noexcept;
+\end{itemdecl}
+
+\begin{itemdescr}
+\pnum
+\effects
+Equivalent to \tcode{*this = !*this}.
+\end{itemdescr}
+
+\indexlibrarymember{swap}{vector<bool>::reference}%
+\begin{itemdecl}
+constexpr void swap(reference x, reference y) noexcept;
+constexpr void swap(reference x, bool& y) noexcept;
+constexpr void swap(bool& x, reference y) noexcept;
+\end{itemdecl}
+
+\begin{itemdescr}
+\pnum
+\effects
+Exchanges the values denoted by \tcode{x} and \tcode{y} as if by:
 
 \begin{codeblock}
 bool b = x;
 x = y;
 y = b;
 \end{codeblock}
+\end{itemdescr}
 
+
+
+\indexlibrarymember{flip}{vector<bool>}%
+\begin{itemdecl}
+constexpr void flip() noexcept;
+\end{itemdecl}
+
+\begin{itemdescr}
+\pnum
+\effects
+Replaces each element in the container with its complement.
 \end{itemdescr}
 
 \begin{itemdecl}

source/future.tex

@@ -636,6 +636,37 @@
 \end{itemize}
 \end{itemdescr}
 
+\rSec1[depr.vector.bool.swap]{Deprecated \tcode{vector<bool, Allocator>} swap}
+
+\pnum
+The following member is declared in addition to those members specified in
+\ref{vector.bool}:
+
+\begin{codeblock}
+namespace std {
+  template<class Allocator> class vector<bool, Allocator> {
+  public:
+    static constexpr void swap(reference x, reference y) noexcept;
+  };
+}
+\end{codeblock}
+
+\indexlibrarymember{swap}{vector<bool>}%
+\begin{itemdecl}
+static constexpr void swap(reference x, reference y) noexcept;
+\end{itemdecl}
+
+\begin{itemdescr}
+\pnum
+\effects
+Exchanges the values denoted by \tcode{x} and \tcode{y} as if by:
+\begin{codeblock}
+bool b = x;
+x = y;
+y = b;
+\end{codeblock}
+\end{itemdescr}
+
 \rSec1[depr.iterator]{Deprecated \tcode{iterator} class template}
 
 \pnum

source/utilities.tex

@@ -10518,13 +10518,18 @@
     // bit reference
     class reference {
     public:
-      constexpr reference(const reference&) = default;
+      constexpr reference(const reference& x) noexcept;
       constexpr ~reference();
       constexpr reference& operator=(bool x) noexcept;              // for \tcode{b[i] = x;}
-      constexpr reference& operator=(const reference&) noexcept;    // for \tcode{b[i] = b[j];}
-      constexpr bool operator~() const noexcept;                    // flips the bit
+      constexpr reference& operator=(const reference& x) noexcept;  // for \tcode{b[i] = b[j];}
+      constexpr const reference& operator=(bool x) const noexcept;
       constexpr operator bool() const noexcept;                     // for \tcode{x = b[i];}
+      constexpr bool operator~() const noexcept;                    // flips the bit
       constexpr reference& flip() noexcept;                         // for \tcode{b[i].flip();}
+
+      friend constexpr void swap(reference x, reference y) noexcept;
+      friend constexpr void swap(reference x, bool& y) noexcept;
+      friend constexpr void swap(bool& x, reference y) noexcept;
     };
 
     // \ref{bitset.cons}, constructors
@@ -10611,7 +10616,7 @@
 zero.
 Each bit has a non-negative position \tcode{pos}.
 When converting
-between an object of class
+between an object of type
 \tcode{bitset<N>}
 and a value of some
 integral type, bit position \tcode{pos} corresponds to the
@@ -10620,6 +10625,84 @@
 The integral value corresponding to two
 or more bits is the sum of their bit values.
 
+\pnum
+\tcode{reference}
+is a class that simulates a reference to a single bit in the sequence.
+
+\indexlibraryctor{bitset::reference}%
+\begin{itemdecl}
+constexpr reference::reference(const reference& x) noexcept;
+\end{itemdecl}
+
+\begin{itemdescr}
+\pnum
+\effects
+Initializes \tcode{*this} to refer to the same bit as \tcode{x}.
+\end{itemdescr}
+
+\indexlibrarydtor{bitset::reference}%
+\begin{itemdecl}
+constexpr reference::~reference();
+\end{itemdecl}
+
+\begin{itemdescr}
+\pnum
+\effects
+None.
+\end{itemdescr}
+
+\indexlibrarymember{operator=}{bitset::reference}%
+\begin{itemdecl}
+constexpr reference& reference::operator=(bool x) noexcept;
+constexpr reference& reference::operator=(const reference& x) noexcept;
+constexpr const reference& reference::operator=(bool x) const noexcept;
+\end{itemdecl}
+
+\begin{itemdescr}
+\pnum
+\effects
+Sets the bit referred to by \tcode{*this} if \tcode{bool(x)} is \tcode{true},
+and clears it otherwise.
+
+\pnum
+\returns
+\tcode{*this}.
+\end{itemdescr}
+
+\indexlibrarymember{swap}{bitset::reference}%
+\begin{itemdecl}
+constexpr void swap(reference x, reference y) noexcept;
+constexpr void swap(reference x, bool& y) noexcept;
+constexpr void swap(bool& x, reference y) noexcept;
+\end{itemdecl}
+
+\begin{itemdescr}
+\pnum
+\effects
+Exchanges the values denoted by \tcode{x} and \tcode{y} as if by:
+
+\begin{codeblock}
+bool b = x;
+x = y;
+y = b;
+\end{codeblock}
+\end{itemdescr}
+
+\indexlibrarymember{flip}{bitset::reference}%
+\begin{itemdecl}
+constexpr reference& reference::flip() noexcept;
+\end{itemdecl}
+
+\begin{itemdescr}
+\pnum
+\effects
+Equivalent to \tcode{*this = !*this}.
+
+\pnum
+\returns
+\tcode{*this}.
+\end{itemdescr}
+
 \pnum
 The functions described in \ref{template.bitset} can report three kinds of
 errors, each associated with a distinct exception: