NAME

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

See also

make_tuple creates a tuple object of the type defined by the argument types
(C++11) (function template)
forward_as_tuple creates a tuple of forwarding references
(C++11) (function template)