Ignoring-Parts-of-a-Value-with-a-Nested-_.cpp

#include "matchit.h"
#include <iostream>
#include <optional>

template <typename T>
std::ostream &operator<<(std::ostream &o, std::optional<T> const &op)
{
  if (op)
  {
    o << *op;
  }
  else
  {
    o << "none";
  }
  return o;
}

void sample1()
{
  auto setting_value = std::make_optional(5);
  auto const new_setting_value = std::make_optional(10);

  using namespace matchit;
  match(setting_value, new_setting_value)(
      pattern | ds(some(_), some(_)) =
          []
      {
        std::cout << "Can't overwrite an existing customized value"
                  << std::endl;
      },
      pattern | _ = [&]
      { setting_value = new_setting_value; });

  std::cout << "setting is " << setting_value << std::endl;
}

void sample2()
{
  auto const numbers = std::make_tuple(2, 4, 8, 16, 32);

  using namespace matchit;
  Id<int32_t> first, third, fifth;
  match(numbers)(pattern | ds(first, _, third, _, fifth) = [&]
                 { std::cout << "Some numbers: " << *first << ", " << *third << ", " << *fifth
                             << std::endl; });
}

int32_t main()
{
  sample1();
  sample2();
  return 0;
}