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cppdraft/tuple/elem.md

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+[tuple.elem]
+
+# 22 General utilities library [[utilities]](./#utilities)
+
+## 22.4 Tuples [[tuple]](tuple#elem)
+
+### 22.4.8 Element access [tuple.elem]
+
+[🔗](#lib:get,tuple)
+
+`template<size_t I, class... Types>
+  constexpr tuple_element_t<I, tuple<Types...>>&
+    get(tuple<Types...>& t) noexcept;
+template<size_t I, class... Types>
+  constexpr tuple_element_t<I, tuple<Types...>>&&
+    get(tuple<Types...>&& t) noexcept;        // #1
+template<size_t I, class... Types>
+  constexpr const tuple_element_t<I, tuple<Types...>>&
+    get(const tuple<Types...>& t) noexcept;   // #2
+template<size_t I, class... Types>
+  constexpr const tuple_element_t<I, tuple<Types...>>&& get(const tuple<Types...>&& t) noexcept;
+`
+
+[1](#1)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/utilities.tex#L2873)
+
+*Mandates*: I < sizeof...(Types)[.](#1.sentence-1)
+
+[2](#2)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/utilities.tex#L2877)
+
+*Returns*: A reference to the Ith element of t, where
+indexing is zero-based[.](#2.sentence-1)
+
+[3](#3)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/utilities.tex#L2882)
+
+[*Note [1](#note-1)*:
+
+For the overload marked #1,
+if a type T in Types is some reference type X&,
+the return type is X&, not X&&[.](#3.sentence-1)
+
+However, if the element type is a non-reference type T,
+the return type is T&&[.](#3.sentence-2)
+
+— *end note*]
+
+[4](#4)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/utilities.tex#L2891)
+
+[*Note [2](#note-2)*:
+
+Constness is shallow[.](#4.sentence-1)
+
+For the overload marked #2,
+if a type T in Types is some reference type X&,
+the return type is X&, not const X&[.](#4.sentence-2)
+
+However, if the element type is a non-reference type T,
+the return type is const T&[.](#4.sentence-3)
+
+This is consistent with how constness is defined to work
+for non-static data members of reference type[.](#4.sentence-4)
+
+— *end note*]
+
+[🔗](#lib:get,tuple_)
+
+`template<class T, class... Types>
+  constexpr T& get(tuple<Types...>& t) noexcept;
+template<class T, class... Types>
+  constexpr T&& get(tuple<Types...>&& t) noexcept;
+template<class T, class... Types>
+  constexpr const T& get(const tuple<Types...>& t) noexcept;
+template<class T, class... Types>
+  constexpr const T&& get(const tuple<Types...>&& t) noexcept;
+`
+
+[5](#5)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/utilities.tex#L2917)
+
+*Mandates*: The type T occurs exactly once in Types[.](#5.sentence-1)
+
+[6](#6)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/utilities.tex#L2921)
+
+*Returns*: A reference to the element of t corresponding to the typeT in Types[.](#6.sentence-1)
+
+[7](#7)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/utilities.tex#L2926)
+
+[*Example [1](#example-1)*: const tuple<int, const int, double, double> t(1, 2, 3.4, 5.6);const int& i1 = get<int>(t); // OK, i1 has value 1const int& i2 = get<const int>(t); // OK, i2 has value 2const double& d = get<double>(t); // error: type double is not unique within t — *end example*]
+
+[8](#8)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/utilities.tex#L2937)
+
+[*Note [3](#note-3)*:
+
+The reason get is a
+non-member function is that if this functionality had been
+provided as a member function, code where the type
+depended on a template parameter would have required using
+the template keyword[.](#8.sentence-1)
+
+— *end note*]