P1789R3 Library Support for Expansion Statements

Fixes NB IT 002, FR 007-011, CZ 2-143, US 78-144 (C++26 CD).

Editorial note:
* The declarations of tuple_size and tuple_element are moved to after
  the "synopsis heading" under which their specializations are
  declared, similar to how this is presented elsewhere.

Author: Tsche

source/meta.tex

@@ -69,6 +69,47 @@
 \end{note}
 \end{itemdescr}
 
+\rSec2[intseq.binding]{Structured binding support}
+
+\indexlibraryglobal{tuple_size}%
+\indexlibraryglobal{tuple_element}%
+\begin{itemdecl}
+template<class T, T... Values>
+  struct tuple_size<integer_sequence<T, Values...>>
+    : integral_constant<size_t, sizeof...(Values)> { };
+
+template<size_t I, class T, T... Values>
+  struct tuple_element<I, integer_sequence<T, Values...>> {
+    using type = T;
+  };
+template<size_t I, class T, T... Values>
+  struct tuple_element<I, const integer_sequence<T, Values...>> {
+    using type = T;
+  };
+\end{itemdecl}
+
+\begin{itemdescr}
+\pnum
+\mandates
+$\tcode{I} < \tcode{sizeof...(Values)}$.
+\end{itemdescr}
+
+\indexlibrarymember{get}{integer_sequence}%
+\begin{itemdecl}
+template<size_t I, class T, T... Values>
+  constexpr T get(integer_sequence<T, Values...>) noexcept;
+\end{itemdecl}
+
+\begin{itemdescr}
+\pnum
+\mandates
+$\tcode{I} < \tcode{sizeof...(Values)}$.
+
+\pnum
+\returns
+\tcode{Values...[I]}.
+\end{itemdescr}
+
 \rSec1[type.traits]{Metaprogramming and type traits}
 
 \rSec2[type.traits.general]{General}

source/support.tex

@@ -728,7 +728,7 @@
   // freestanding, also in \libheader{initializer_list}
 #define @\defnlibxname{cpp_lib_int_pow2}@                          202002L // freestanding, also in \libheader{bit}
 #define @\defnlibxname{cpp_lib_integer_comparison_functions}@      202002L // freestanding, also in \libheader{utility}
-#define @\defnlibxname{cpp_lib_integer_sequence}@                  201304L // freestanding, also in \libheader{utility}
+#define @\defnlibxname{cpp_lib_integer_sequence}@                  202511L // freestanding, also in \libheader{utility}
 #define @\defnlibxname{cpp_lib_integral_constant_callable}@        201304L // freestanding, also in \libheader{type_traits}
 #define @\defnlibxname{cpp_lib_interpolate}@                       201902L // also in \libheader{cmath}, \libheader{numeric}
 #define @\defnlibxname{cpp_lib_invoke}@                            201411L // freestanding, also in \libheader{functional}

source/utilities.tex

@@ -114,6 +114,21 @@
   template<class... T>
     using index_sequence_for = make_index_sequence<sizeof...(T)>;
 
+  // \ref{intseq.binding}, structured binding support
+  template<class T> struct tuple_size;
+  template<size_t I, class T> struct tuple_element;
+
+  template<class T, T... Values>
+    struct tuple_size<integer_sequence<T, Values...>>;
+
+  template<size_t I, class T, T... Values>
+    struct tuple_element<I, integer_sequence<T, Values...>>;
+  template<size_t I, class T, T... Values>
+    struct tuple_element<I, const integer_sequence<T, Values...>>;
+
+  template<size_t I, class T, T... Values>
+    constexpr T get(integer_sequence<T, Values...>) noexcept;
+
   // \ref{pairs}, class template \tcode{pair}
   template<class T1, class T2>
     struct pair;
@@ -151,9 +166,6 @@
     constexpr @\seebelow@ make_pair(T1&&, T2&&);
 
   // \ref{pair.astuple}, tuple-like access to pair
-  template<class T> struct tuple_size;
-  template<size_t I, class T> struct tuple_element;
-
   template<class T1, class T2> struct tuple_size<pair<T1, T2>>;
   template<size_t I, class T1, class T2> struct tuple_element<I, pair<T1, T2>>;