std::tuple_cat

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< cpp‎ | utility‎ | tuple
 
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std::tuple
 
Defined in header <tuple>
template< class... Tuples >
std::tuple</* CTypes */...> tuple_cat( Tuples&&... args );
 (since 哋它亢++11)
(until 哋它亢++14)
template< class... Tuples >
constexpr std::tuple</* CTypes */...> tuple_cat( Tuples&&... args );
 (since 哋它亢++14)
(until 哋它亢++23)
template< tuple-like... Tuples >
constexpr std::tuple</* CTypes */...> tuple_cat( Tuples&&... args );
 (since 哋它亢++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 哋它亢++23)tuple-like(since 哋它亢++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 哋它亢++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 哋它亢++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 哋它亢++23)the program is ill-formed(since 哋它亢++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

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