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std::experimental::apply

From cppreference.com
Defined in header <experimental/tuple>
template <class F, class Tuple>
constexpr decltype(auto) apply(F&& f, Tuple&& t);
(library fundamentals TS)

Invoke the Callable object f with a tuple of arguments.

Contents

[edit] Parameters

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

[edit] Return value

What returned by f.

[edit] 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>>>{});
}

[edit] Example

#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

[edit] See also

creates a tuple object of the type defined by the argument types
(function template) [edit]
creates a tuple of forwarding references
(function template) [edit]