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+[tuple.helper]
+
+# 22 General utilities library [[utilities]](./#utilities)
+
+## 22.4 Tuples [[tuple]](tuple#helper)
+
+### 22.4.7 Tuple helper classes [tuple.helper]
+
+[ð](#lib:tuple_size,in_general)
+
+`template<class T> struct tuple_size;
+`
+
+[1](#1)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/utilities.tex#L2761)
+
+Except where specified otherwise,
+all specializations of tuple_size meet the[*Cpp17UnaryTypeTrait*](meta.rqmts#:Cpp17UnaryTypeTrait "21.3.2 Requirements [meta.rqmts]") requirements ([[meta.rqmts]](meta.rqmts "21.3.2 Requirements")) with a
+base characteristic of integral_constant<size_t, N> for some N[.](#1.sentence-1)
+
+[ð](#lib:tuple_size)
+
+`template<class... Types>
+  struct tuple_size<tuple<Types...>> : integral_constant<size_t, sizeof...(Types)> { };
+`
+
+[ð](#lib:tuple_element)
+
+`template<size_t I, class... Types>
+  struct tuple_element<I, tuple<Types...>> {
+    using type = TI;
+  };
+`
+
+[2](#2)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/utilities.tex#L2784)
+
+*Mandates*: I < sizeof...(Types)[.](#2.sentence-1)
+
+[3](#3)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/utilities.tex#L2788)
+
+*Type*: TI is the
+type of the Ith element of Types,
+where indexing is zero-based[.](#3.sentence-1)
+
+[ð](#lib:tuple_size_)
+
+`template<class T> struct tuple_size<const T>;
+`
+
+[4](#4)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/utilities.tex#L2801)
+
+Let TS denote tuple_size<T> of the cv-unqualified type T[.](#4.sentence-1)
+
+If the expression TS::value is well-formed
+when treated as an [unevaluated operand](expr.context#def:unevaluated_operand "7.2.3 Context dependence [expr.context]"), then
+each specialization of the template meets the [*Cpp17UnaryTypeTrait*](meta.rqmts#:Cpp17UnaryTypeTrait "21.3.2 Requirements [meta.rqmts]") requirements ([[meta.rqmts]](meta.rqmts "21.3.2 Requirements"))
+with a base characteristic ofintegral_constant<size_t, TS::value>
+
+Otherwise, it has no member value[.](#4.sentence-3)
+
+[5](#5)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/utilities.tex#L2812)
+
+Access checking is performed as if in a context
+unrelated to TS and T[.](#5.sentence-1)
+
+Only the validity of the immediate context of the expression is considered[.](#5.sentence-2)
+
+[*Note [1](#note-1)*:
+
+The compilation of the expression can result in side effects
+such as the instantiation of class template specializations and
+function template specializations, the generation of implicitly-defined functions, and so on[.](#5.sentence-3)
+
+Such side effects are not in the âimmediate contextâ and
+can result in the program being ill-formed[.](#5.sentence-4)
+
+â *end note*]
+
+[6](#6)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/utilities.tex#L2824)
+
+In addition to being available via inclusion of the [<tuple>](tuple.syn#header:%3ctuple%3e "22.4.2 Header <tuple> synopsis [tuple.syn]") header,
+the template is available
+when any of the headers[<array>](array.syn#header:%3carray%3e "23.3.2 Header <array> synopsis [array.syn]"),[<ranges>](ranges.syn#header:%3cranges%3e "25.2 Header <ranges> synopsis [ranges.syn]"), or[<utility>](utility.syn#header:%3cutility%3e "22.2.1 Header <utility> synopsis [utility.syn]") are included[.](#6.sentence-1)
+
+[ð](#lib:tuple_element_)
+
+`template<size_t I, class T> struct tuple_element<I, const T>;
+`
+
+[7](#7)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/utilities.tex#L2840)
+
+Let TE denote tuple_element_t<I, T> of the cv-unqualified type T[.](#7.sentence-1)
+
+Then
+each specialization of the template meets the [*Cpp17TransformationTrait*](meta.rqmts#:Cpp17TransformationTrait "21.3.2 Requirements [meta.rqmts]") requirements ([[meta.rqmts]](meta.rqmts "21.3.2 Requirements"))
+with a member typedef type that names the type add_const_t<TE>[.](#7.sentence-2)
+
+[8](#8)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/utilities.tex#L2845)
+
+In addition to being available via inclusion of the [<tuple>](tuple.syn#header:%3ctuple%3e "22.4.2 Header <tuple> synopsis [tuple.syn]") header,
+the template is available
+when any of the headers[<array>](array.syn#header:%3carray%3e "23.3.2 Header <array> synopsis [array.syn]"),[<ranges>](ranges.syn#header:%3cranges%3e "25.2 Header <ranges> synopsis [ranges.syn]"), or[<utility>](utility.syn#header:%3cutility%3e "22.2.1 Header <utility> synopsis [utility.syn]") are included[.](#8.sentence-1)