Rest-pattern.cpp

#include "matchit.h"
#include <iostream>
#include <vector>
using namespace matchit;

template <typename T>
std::ostream &operator<<(std::ostream &o, Subrange<T> const &subrange)
{
  o << " [ ";
  for (auto const &e : subrange)
  {
    o << e << ", ";
  }
  o << " ] ";
  return o;
}

void sample()
{
  auto const words = std::vector<std::string>{"a", "b", "c"};
  auto const &slice = words;
  Id<std::string> head;
  Id<SubrangeT<std::vector<std::string> const>> tail;
  match(slice)(
      // clang-format off
        pattern | ds()                   = [&] { std::cout << "slice is empty" << std::endl; },
        pattern | ds(head)               = [&] { std::cout << "single element " << *head << std::endl; },
        pattern | ds(head, tail.at(ooo))  = [&] { std::cout << "head=" << *head << " tail=" << *tail << std::endl; }
      // clang-format on
  );

  Id<SubrangeT<std::vector<std::string> const>> subrange;
  match(slice)(
      // clang-format off
        // Ignore everything but the last element, which must be "!".
        pattern | ds(ooo, "!")              = [&] { std::cout << "!!!" << std::endl; },

        // `subrange` is a slice of everything except the last element, which must be "z".
        pattern | ds(subrange.at(ooo), "z") = [&] { std::cout << "starts with: " << *subrange << std::endl; },

        // `subrange` is a slice of everything but the first element, which must be "a".
        pattern | ds("a", subrange.at(ooo)) = [&] { std::cout << "ends with: " << *subrange << std::endl; },

        pattern | ds(subrange.at(ooo))      = [&] { std::cout << *subrange << std::endl; }
      // clang-format on
  );

  Id<std::string> penultimate;
  match(slice)(
      // clang-format off
        pattern | ds(ooo, penultimate, _) = [&] { std::cout << "next to last is " << *penultimate << std::endl; }
      // clang-format on
  );

  constexpr auto tuple = std::make_tuple(1, 2, 3, 4, 5);
  // Rest patterns may also be used in tuple and tuple struct patterns.
  Id<int32_t> y, z;
  match(tuple)(
      // clang-format off
        pattern | ds(1, ooo, y, z) = [&] { std::cout << "y=" << *y << " z=" << *z << std::endl; },
        pattern | ds(ooo, 5      ) = [&] { std::cout << "tail must be 5" << std::endl; },
        pattern | ds(ooo         ) = [&] { std::cout << "matches everything else" << std::endl; }
      // clang-format on
  );
}

int32_t main()
{
  sample();
  return 0;
}