With the introduction of Coroutine in C++20, developers are now able to write more efficient and readable asynchronous code. However, migrating existing codebases to leverage this new feature can sometimes be challenging. In this blog post, we will explore some strategies to migrate code that utilizes older techniques to leverage the power of Coroutines in different versions of C++.

Understanding the Basics

Before diving into migration strategies, let’s quickly recap what Coroutines are and why they are useful. Coroutines are a way to write asynchronous code that resembles synchronous code, making it more readable and maintainable. They allow developers to suspend and resume execution at specified points without blocking the thread.

C++11/14 to C++17

The first step in migrating code that doesn’t use Coroutines is to upgrade the project to C++17, which introduced the std::experimental::coroutine header. Although this is still not as powerful as the full Coroutine support provided in C++20, it allows you to start using Coroutines with minimal changes.

To migrate your code, follow these steps:

1. Replace functions that need to be coroutines with a std::experimental::generator or a custom implementation of a coroutine type.
2. Replace std::future with std::experimental::future or other similar libraries that provide Coroutine support.
3. Modify the code to use the new Coroutine syntax, such as co_yield, co_await, and co_return.

This process may involve refactoring significant portions of the codebase, but it provides a smooth transition to using Coroutines.

C++17 to C++20

If you have already migrated your code to C++17 and want to take full advantage of the Coroutine features introduced in C++20, there are a few additional steps you can take:

1. Update your code to use the standardized Coroutine facilities provided by C++20, such as std::coroutine_handle and std::suspend_never.
2. Remove any dependencies on experimental libraries and replace them with the standard Coroutine features.
3. Utilize the new co_return syntax to improve the readability of your code.

This migration process requires updating the codebase to use the latest C++20 standards and removing any deprecated or experimental features related to Coroutines.

Conclusion

Migrating code to adopt Coroutines in different versions of C++ can provide significant benefits in terms of code readability and performance. Upgrading your codebase incrementally, from C++11/14 to C++17 and then to C++20, allows you to take advantage of Coroutines gradually. By following the strategies outlined in this blog post, you can modernize your code and harness the power of Coroutines in your C++ projects.

#cpp #coroutines #C++20 #migration