cppdraft_translate/cppdraft/tuple/creation.md

[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)