NAME¶

std::make_tuple - std::make_tuple

Synopsis¶

Defined in header <tuple>
template< class... Types > (since C++11)
std::tuple<VTypes...> make_tuple( Types&&... args ); (constexpr since C++14)

Creates a tuple object, deducing the target type from the types of arguments.

For each Ti in Types..., the corresponding type Vi in VTypes... is
std::decay<Ti>::type unless application of std::decay results in
std::reference_wrapper<X> for some type X, in which case the deduced type is X&.

Parameters¶

args - zero or more arguments to construct the tuple from

Return value¶

A std::tuple object containing the given values, created as if by
std::tuple<VTypes...>(std::forward<Types>(t)...).

Possible implementation¶

template <class T>
struct unwrap_refwrapper
{
using type = T;
};

template <class T>
struct unwrap_refwrapper<std::reference_wrapper<T>>
{
using type = T&;
};

template <class T>
using unwrap_decay_t = typename unwrap_refwrapper<typename std::decay<T>::type>::type;
// or use std::unwrap_ref_decay_t (since C++20)

template <class... Types>
constexpr // since C++14
std::tuple<unwrap_decay_t<Types>...> make_tuple(Types&&... args)
{
return std::tuple<unwrap_decay_t<Types>...>(std::forward<Types>(args)...);
}

Example¶

// Run this code

#include <iostream>
#include <tuple>
#include <functional>

std::tuple<int, int> f() // this function returns multiple values
{
int x = 5;
return std::make_tuple(x, 7); // return {x,7}; in C++17
}

int main()
{
// heterogeneous tuple construction
int n = 1;
auto t = std::make_tuple(10, "Test", 3.14, std::ref(n), n);
n = 7;
std::cout << "The value of t is " << "("
<< std::get<0>(t) << ", " << std::get<1>(t) << ", "
<< std::get<2>(t) << ", " << std::get<3>(t) << ", "
<< std::get<4>(t) << ")\n";

// function returning multiple values
int a, b;
std::tie(a, b) = f();
std::cout << a << " " << b << "\n";
}

Output:¶

The value of t is (10, Test, 3.14, 7, 1)
5 7

See also¶

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)
tuple_cat creates a tuple by concatenating any number of tuples
(C++11) (function template)
apply calls a function with a tuple of arguments
(C++17) (function template)