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std::make_tuple

From cppreference.com
< cpp‎ | utility‎ | tuple

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

Contents

[edit] Parameters

args - zero or more arguments to construct the tuple from

[edit] Return value

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

[edit] Possible implementation

template <class T>
struct special_decay
{
    using type = typename std::decay<T>::type;
};
 
template <class T>
struct special_decay<std::reference_wrapper<T>>
{
    using type = T&;
};
 
template <class T>
using special_decay_t = typename special_decay<T>::type;
 
template <class... Types>
auto make_tuple(Types&&... args)
{
    return std::tuple<special_decay_t<Types>...>(std::forward<Types>(args)...);
}

[edit] Example

#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); // not "return {x,7};" because the corresponding
                                  // tuple constructor is explicit (LWG 2051)
}
 
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 t1 is (10, Test, 3.14, 7, 1)
5 7
creates a tuple of lvalue references or unpacks a tuple into individual objects
(function template) [edit]
creates a tuple of rvalue references
(function template) [edit]
creates a tuple by concatenating any number of tuples
(function template) [edit]