Std::experimental::apply (3) Linux Manual Page

std::experimental::apply – std::experimental::apply

Synopsis

Defined in header <experimental/tuple>

template <class F, class Tuple>                    (library fundamentals TS)

constexpr decltype(auto) apply(F&& f, Tuple&& t);

Invoke the Callable object f with a tuple of arguments.

Parameters

f – Callable object to be invoked
t – tuple whose elements to be used as arguments to f

Return value

What returned by f.

Possible implementation

  namespace detail {
  template <class F, class Tuple, std::size_t… I>
  constexpr decltype(auto) apply_impl( F&& f, Tuple&& t, std::index_sequence<I…> )
  {
    return std::invoke(std::forward<F>(f), std::get<I>(std::forward<Tuple>(t))…);
    // Note: std::invoke is a C++17 feature
  }
  } // namespace detail

  template <class F, class Tuple>
  constexpr decltype(auto) apply(F&& f, Tuple&& t)
  {
      return detail::apply_impl(std::forward<F>(f), std::forward<Tuple>(t),
          std::make_index_sequence<std::tuple_size_v<std::decay_t<Tuple>>>{});
  }

Example

// Run this code

#include <iostream>

#include <tuple>
template <typename... Ts>

void print_tuple(const std::tuple<Ts...> &tuple)

{
    std::apply([](const auto &...elem) {
        ((std::cout << elem << '\n'), ...);
    },
               tuple);
}
int main()
{
    const std::tuple<int, char> t = std::make_tuple(5, 'a');
    print_tuple(t);
}

Output:

5
a

std::experimental::apply (3) Linux Manual Page