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cppdraft/tuple/creation.md

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+[tuple.creation]
+
+# 22 General utilities library [[utilities]](./#utilities)
+
+## 22.4 Tuples [[tuple]](tuple#creation)
+
+### 22.4.5 Tuple creation functions [tuple.creation]
+
+[🔗](#lib:make_tuple)
+
+`template<class... TTypes>
+  constexpr tuple<unwrap_ref_decay_t<TTypes>...> make_tuple(TTypes&&... t);
+`
+
+[1](#1)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/utilities.tex#L2579)
+
+*Returns*: tuple<unwrap_ref_decay_t<TTypes>...>(std​::​forward<TTypes>(t)...)[.](#1.sentence-1)
+
+[2](#2)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/utilities.tex#L2583)
+
+[*Example [1](#example-1)*:
+
+int i; float j;
+make_tuple(1, ref(i), cref(j)); creates a tuple of type tuple<int, int&, const float&>[.](#2.sentence-1)
+
+— *end example*]
+
+[🔗](#lib:forward_as_tuple)
+
+`template<class... TTypes>
+  constexpr tuple<TTypes&&...> forward_as_tuple(TTypes&&... t) noexcept;
+`
+
+[3](#3)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/utilities.tex#L2601)
+
+*Effects*: Constructs a tuple of references to the arguments in t suitable
+for forwarding as arguments to a function[.](#3.sentence-1)
+
+Because the result may contain references
+to temporary objects, a program shall ensure that the return value of this
+function does not outlive any of its arguments (e.g., the program should typically
+not store the result in a named variable)[.](#3.sentence-2)
+
+[4](#4)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/utilities.tex#L2609)
+
+*Returns*: tuple<TTypes&&...>(std​::​forward<TTypes>(t)...)[.](#4.sentence-1)
+
+[🔗](#lib:tie)
+
+`template<class... TTypes>
+  constexpr tuple<TTypes&...> tie(TTypes&... t) noexcept;
+`
+
+[5](#5)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/utilities.tex#L2623)
+
+*Returns*: tuple<TTypes&...>(t...)[.](#5.sentence-1)
+
+[6](#6)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/utilities.tex#L2627)
+
+[*Example [2](#example-2)*:
+
+tie functions allow one to create tuples that unpack
+tuples into variables[.](#6.sentence-1)
+
+ignore can be used for elements that
+are not needed:int i; std::string s;
+tie(i, ignore, s) = make_tuple(42, 3.14, "C++");// i == 42, s == "C++"
+
+— *end example*]
+
+[🔗](#lib:tuple_cat)
+
+`template<[tuple-like](tuple.like#concept:tuple-like "22.4.3 Concept tuple-like [tuple.like]")... Tuples>
+  constexpr tuple<CTypes...> tuple_cat(Tuples&&... tpls);
+`
+
+[7](#7)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/utilities.tex#L2647)
+
+Let n be sizeof...(Tuples)[.](#7.sentence-1)
+
+For every integer 0≤i<n:
+
+- [(7.1)](#7.1)
+
+  Let Ti be the ith type in Tuples[.](#7.1.sentence-1)
+
+- [(7.2)](#7.2)
+
+  Let Ui be remove_cvref_t<Ti>[.](#7.2.sentence-1)
+
+- [(7.3)](#7.3)
+
+  Let tpi be the ith element
+in the function parameter pack tpls[.](#7.3.sentence-1)
+
+- [(7.4)](#7.4)
+
+  Let Si be tuple_size_v<Ui>[.](#7.4.sentence-1)
+
+- [(7.5)](#7.5)
+
+  Let Eki be tuple_element_t<k, Ui>[.](#7.5.sentence-1)
+
+- [(7.6)](#7.6)
+
+  Let eki be get<k>(std​::​forward<Ti>(tpi))[.](#7.6.sentence-1)
+
+- [(7.7)](#7.7)
+
+  Let Elemsi be a pack of the types E0i,…,ESi−1i[.](#7.7.sentence-1)
+
+- [(7.8)](#7.8)
+
+  Let elemsi be a pack of the expressions e0i,…,eSi−1i[.](#7.8.sentence-1)
+
+The types in CTypes are equal to the ordered sequence of
+the expanded packs of typesElems0..., Elems1..., …, Elemsn−1...[.](#7.sentence-3)
+
+Let celems be the ordered sequence of
+the expanded packs of expressionselems0..., …, elemsn−1...[.](#7.sentence-4)
+
+[8](#8)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/utilities.tex#L2676)
+
+*Mandates*: (is_constructible_v<CTypes, decltype(celems)> && ...) is true[.](#8.sentence-1)
+
+[9](#9)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/utilities.tex#L2680)
+
+*Returns*: tuple<CTypes...>(celems...)[.](#9.sentence-1)