# std::tuple_cat

From cppreference.com
< cpp‎ | utility‎ | tuple

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

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 choose to support types (such as std::array and std::pair) that follow the tuple-like protocol. | (until C++23)
The types std::decay_t <Tuples>... are constrained to be tuple-like, i.e. each type therein is required to be a specialization of std::tuple or another type (such as std::array and std::pair) that models `tuple-like`. | (since C++23)

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

Retrieved from "https://en.cppreference.com/mwiki/index.php?title=cpp/utility/tuple/tuple_cat&oldid=151757"