NAME¶

std::tuple_cat - std::tuple_cat

Synopsis¶

Defined in header <tuple>
template< class... Tuples > (since C++11)
std::tuple</* CTypes */...> tuple_cat( Tuples&&... args ); (until C++14)
template< class... Tuples > (since C++14)
constexpr std::tuple</* CTypes */...> tuple_cat( Tuples&&... args ); (until C++23)
template< tuple-like... Tuples > (since C++23)
constexpr std::tuple</* CTypes */...> tuple_cat( Tuples&&... args );

Constructs a tuple that is a concatenation of all tuples in args. The element types
/* CTypes */ of the returned tuple is formed by concatenating the elements type
packs of all
std::tuple
(until C++23)
tuple-like
(since C++23) types in Tuples in order.

The behavior is undefined if any type in std::decay_t<Tuples>... is
not a specialization of std::tuple. However, an implementation may (until C++23)
choose to support types (such as std::array and std::pair) that follow
the tuple-like protocol.
The types std::decay_t<Tuples>... are constrained to be tuple-like,
i.e. each type therein is required to be a specialization of (since C++23)
std::tuple or another type (such as std::array and std::pair) that
models tuple-like.

If any type in /* CTypes */ is not constructible from the type of the corresponding
element in the sequence of elements concatenated from args,
the behavior is undefined
(until C++23)
the program is ill-formed
(since C++23).

Parameters¶

args - zero or more tuples to concatenate

Return value¶

A std::tuple object composed of all elements of all argument tuples constructed from
std::get<j>(std::forward<Ti>(arg)) for each individual element.

Example¶

// Run this code

#include <iostream>
#include <string>
#include <tuple>

// helper function to print a tuple of any size
template<class Tuple, std::size_t N>
struct TuplePrinter
{
static void print(const Tuple& t)
{
TuplePrinter<Tuple, N - 1>::print(t);
std::cout << ", " << std::get<N-1>(t);
}
};

template<class Tuple>
struct TuplePrinter<Tuple, 1>
{
static void print(const Tuple& t)
{
std::cout << std::get<0>(t);
}
};

template<typename... Args, std::enable_if_t<sizeof...(Args) == 0, int> = 0>
void print(const std::tuple<Args...>& t)
{
std::cout << "()\n";
}

template<typename... Args, std::enable_if_t<sizeof...(Args) != 0, int> = 0>
void print(const std::tuple<Args...>& t)
{
std::cout << "(";
TuplePrinter<decltype(t), sizeof...(Args)>::print(t);
std::cout << ")\n";
}
// end helper function

int main()
{
std::tuple<int, std::string, float> t1(10, "Test", 3.14);
int n = 7;
auto t2 = std::tuple_cat(t1, std::make_tuple("Foo", "bar"), t1, std::tie(n));
n = 42;
print(t2);
}

Output:¶

(10, Test, 3.14, Foo, bar, 10, Test, 3.14, 42)

See also¶

make_tuple creates a tuple object of the type defined by the argument types
(C++11) (function template)
tie creates a tuple of lvalue references or unpacks a tuple into
(C++11) individual objects
(function template)
forward_as_tuple creates a tuple of forwarding references
(C++11) (function template)