//********************************************************
// The following code example is taken from the book
//  C++23 - The Complete Guide
//  by Nicolai M. Josuttis (www.josuttis.com)
//  https://www.cppstd23.com
//
// The code is licensed under a
//  Creative Commons Attribution 4.0 International License
//  https://creativecommons.org/licenses/by/4.0/
//********************************************************


#include <iostream>
#include <array>
#include <utility>
#include <cstddef>     // for std::byte
#include <memory>
#include <memory_resource>
#include <generator>

// coroutine using passed memory resource to hold its state:
std::pmr::generator<long> fibonacci(std::allocator_arg_t,
                                    std::pmr::polymorphic_allocator<>,
                                    int num) 
{
  // first two numbers are 1:               
  long a = 1;
  long b = 1;
  co_yield a;       // SUSPEND with first number
  co_yield b;       // SUSPEND with second number
  // loop over sums of previous two numbers:
  for (int i = 0; i < num-2; ++i) {
    auto sum = a + b;
    co_yield sum;   // SUSPEND with third to num-th number
    a = std::exchange(b, sum);
  }
}

int main() 
{
  // memory pool operating on 1k memory on the stack:
  std::array<std::byte, 1'000> buf;
  std::pmr::monotonic_buffer_resource pool{buf.data(), buf.size(),
                                           std::pmr::null_memory_resource()};

  // call coroutine using the memory pool:
  for (auto val : fibonacci(std::allocator_arg, &pool, 10)) {
    std::cout << val << ' ';
  }
  std::cout << '\n';
}