#include <cassert>
#include <iostream>
#include <ostream>
// requires C++23 to compile
class A {
  long long counter = 0;

public:
  A() : counter{0} {}
  A operator()() {
    A ret = *this;
    ret.counter++;
    return ret;
  }
  // requires C++23 to compile
  A operator[](int _ = 0) {
    A ret = *this;
    ret.counter--;
    return ret;
  }
  // friend std::ostream &operator<<(std::ostream &lhs, A const &rhs) {
  //   lhs << rhs.counter;
  //   return lhs;
  // }
  operator long long() { return counter; }
};

int main(void) {
  A a;
  assert(a == 0);
  assert(a[] == -1);
  assert(a[]() == 0);
  assert(a[]()() == 1);
  int i = a;
  assert(i == 0);
  i = a()()();
  assert(i == 3);
  return 0;
}