In the function descriptions that follow, the members of a parameter pack XTypes are denoted by Xi for i in [0, sizeof...(XTypes)) in order, where indexing is zero-based.
constexpr tuple<VTypes...> make_tuple(TTypes&&... t);
The pack VTypes is defined as follows. Let Ui be decay_t<Ti> for each Ti in TTypes. If Ui is a specialization of reference_wrapper, then Vi in VTypes is Ui::type&, otherwise Vi is Ui.
int i; float j; make_tuple(1, ref(i), cref(j))
creates a tuple of type tuple<int, int&, const float&>. — end example ]
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 variables, 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).
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: 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 <class... Tuples>
constexpr tuple<CTypes...> tuple_cat(Tuples&&... tpls);
In the following paragraphs, let Ti be the ith type in Tuples, Ui be remove_reference_t<Ti>, and tpi be the ith parameter in the function parameter pack tpls, where all indexing is zero-based.
Requires: For all i, Ui shall be the type cvi tuple<Argsi...>, where cvi is the (possibly empty) ith cv-qualifier-seq and Argsi is the parameter pack representing the element types in Ui. Let Aik be the kth type in Argsi. For all Aik the following requirements shall be satisfied:
If Ti is deduced as an lvalue reference type, then is_constructible_v<Aik, cviAik&> == true, otherwise
is_constructible_v<Aik, cviAik&&> == true.
Remarks: The types in CTypes shall be equal to the ordered sequence of the extended types Args0..., Args1..., …, Argsn−1..., where n is equal to sizeof...(Tuples). Let ei... be the ith ordered sequence of tuple elements of the resulting tuple object corresponding to the type sequence Argsi.
Returns: A tuple object constructed by initializing the kith type element eik in ei... with
for each valid ki and each group ei in order.