Coroutines are a powerful feature in C++ that allow for more expressive and efficient asynchronous programming. They provide a way to suspend and resume execution of a function, allowing for tasks to be paused and resumed without blocking the entire program. In this blog post, we will explore how to define a coroutine in C++.

Prerequisites

Before we dive into defining a coroutine, make sure you are using a C++20 compliant compiler. Also, be familiar with the concept of coroutines and their benefits in asynchronous programming.

Defining a Coroutine

In C++, coroutines are defined using generators. A generator is a special type of function that can be suspended and resumed. To define a coroutine, follow these steps:

1. Include the <coroutine> header file, which contains the necessary coroutine library.

#include <coroutine>

1. Define a function with the coroutine keyword and the return type std::coroutine_handle<>. This function will act as our coroutine.

std::coroutine_handle<> myCoroutine() {
  // Coroutine logic goes here
}

1. Inside the coroutine function, use the co_yield keyword to specify points where the coroutine should suspend and return a value. This allows the caller to resume the coroutine later.

std::coroutine_handle<> myCoroutine() {
  co_yield 1;
  co_yield 2;
  co_yield 3;
}

1. To make the coroutine usable, create a generator object using std::coroutine_handle::from_address and call the resume function on it.

std::coroutine_handle<> coroutine = myCoroutine();
coroutine.resume();

1. To clean up resources, make sure to call coroutine.destroy() when you are done with the coroutine to avoid memory leaks.

coroutine.destroy();

Conclusion

Defining coroutines in C++ allows for more flexible and efficient asynchronous programming. By using generators and the co_yield keyword, you can easily suspend and resume execution of a function. Remember to include the <coroutine> header file and use a C++20 compliant compiler to take advantage of this feature.

#coroutines #asynchronousprogramming