std::make_tuple (3) - Linux Manuals

std::make_tuple: std::make_tuple

NAME

std::make_tuple - std::make_tuple

Synopsis

Defined in header <tuple>
template< class... Types > (since C++11)
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 special_decay_t = typename unwrap_refwrapper<typename std::decay<T>::type>::type;

  template <class... Types>
  auto make_tuple(Types&&... args)
  {
      return std::tuple<special_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