Class test_visitor_three

test_visit_struct.cpp:114–136

struct test_visitor_three {
  int result = 0;

  template <typename T>
  void operator()(const char *, T &&) {}

  void operator()(const char *, int &) {
    result = 1;
  }

  void operator()(const char *, const int &) {
    result = 2;
  }

  void operator()(const char *, int &&) {
    result = 3;
  }

  // Make it non-copyable and non-moveable, apply visitor should still work.
  test_visitor_three() = default;
  test_visitor_three(const test_visitor_three &) = delete;
  test_visitor_three(test_visitor_three &&) = delete;
};


// Some binary visitors for test