22 General utilities library [utilities]

22.4 Tuples [tuple]

22.4.5 Tuple creation functions [tuple.creation]

template<class... TTypes> constexpr tuple<unwrap_ref_decay_t<TTypes>...> make_tuple(TTypes&&... t);
Returns: tuple<unwrap_­ref_­decay_­t<TTypes>...>(std​::​forward<TTypes>(t)...).
[Example 1:
int i; float j; make_tuple(1, ref(i), cref(j)); creates a tuple of type tuple<int, int&, const float&>.
— end example]
template<class... TTypes> constexpr tuple<TTypes&&...> forward_as_tuple(TTypes&&... t) noexcept;
Effects: Constructs a tuple of references to the arguments in t suitable for forwarding as arguments to a function.
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).
Returns: tuple<TTypes&&...>(std​::​forward<TTypes>(t)...).
template<class... TTypes> constexpr tuple<TTypes&...> tie(TTypes&... t) noexcept;
Returns: tuple<TTypes&...>(t...).
When an argument in t is ignore, assigning any value to the corresponding tuple element has no effect.
[Example 2:
tie functions allow one to create tuples that unpack tuples into variables.
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]
template<tuple-like... Tuples> constexpr tuple<CTypes...> tuple_cat(Tuples&&... tpls);
Let n be sizeof...(Tuples).
For every integer :
  • Let be the type in Tuples.
  • Let be remove_­cvref_­t<>.
  • Let be the element in the function parameter pack tpls.
  • Let be tuple_­size_­v<>.
  • Let be tuple_­element_­t<k, >.
  • Let be get<k>(std​::​forward<>()).
  • Let be a pack of the types .
  • Let be a pack of the expressions .
The types in CTypes are equal to the ordered sequence of the expanded packs of types ..., ..., …, ....
Let celems be the ordered sequence of the expanded packs of expressions ..., …, ....
Mandates: (is_­constructible_­v<CTypes, decltype(celems)> && ...) is true.
Returns: tuple<CTypes...>(celems...).