fig18_01.cpp

// fig18_01.cpp
// Creating a generator coroutine with co_yield.
#include <fmt/format.h>
#include <iostream>
#include <sstream>
#include <thread> 
#include <tl/generator.hpp>

// get current thread's ID as a string
std::string id() {
   std::ostringstream out;
   out << std::this_thread::get_id();
   return out.str();
}

// coroutine that repeatedly yields the next Fibonacci value in sequence
tl::generator<int> fibonacciGenerator(int limit) {
   std::cout << fmt::format(
      "Thread {}: fibonacciGenerator started executing\n", id());

   int value1{0}; // Fibonacci(0)
   int value2{1}; // Fibonacci(1)

   for (int i{0}; i < limit; ++i) {
      co_yield value1; // yield current value of value1

      // update value1 and value2 for next iteration
      int temp{value1 + value2};
      value1 = value2;
      value2 = temp;
   }

   std::cout << fmt::format(
      "Thread {}: fibonacciGenerator finished executing\n", id());
}

int main() {
   std::cout << fmt::format("Thread {}: main begins\n", id());

   // display first 10 Fibonacci values 
   for (int i{0}; auto value : fibonacciGenerator(10)) {
      std::cout << fmt::format("Fibonacci({}) is {}\n", i++, value);
   }  

   std::cout << fmt::format("Thread {}: main ends\n", id());
}




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