operator[]() [4/4]

template<typename... Ts>

template<kumi::str L>
requires (kumi::concepts::contains_label<kumi::label_t<L>, Ts...>)

decltype(auto) kumi::tuple< Ts >::operator[] ( kumi::label_t< L > s ) &

inlineconstexprnoexcept

Extracts the element of the field labeled L from a kumi::tuple.

Note

Does not participate in overload resolution if the label is not present in the tuple

Parameters

s	label of the field to access

Returns

A reference to the element of the selected field of current tuple.

Example:

#include <kumi/kumi.hpp>
#include <iostream>
 
struct my_id : kumi::identifier<my_id>
{
  using parent = kumi::identifier<my_id>;
  using parent::operator=;
 
  friend constexpr auto to_str(my_id) { return kumi::str{"mystery"}; }
};
 
inline constexpr my_id my_field{};
 
int main()
{
  using namespace kumi::literals;
 
  kumi::tuple t = { "x"_id = 1, 2.3, my_field = '@' };
  std::cout << t << "\n";
 
  std::cout << t["x"_l] << "\n";
  std::cout << t["mystery"_l] << "\n";
 
  t["mystery"_l]++;
  std::cout << t["mystery"_l] << "\n";
}