A first step.

C++20 Coroutines

by Martin Bond

From the article:

There seems to be a lot of confusion around the implementation of C++20 coroutines, which I think is due to the draft technical specification for C++20 stating that coroutines are a work in progress so we can’t expect full compiler and library support at this point in time.

A lot of the problems probably arise from the lack of official documentation about working with coroutines. We have been given C++ syntax support for coroutines (the co_yield and co_return) but without all of what I consider full library support. The standard library has hooks and basic functionality for supporting coroutines, but we must incorporate this into our own classes. I anticipate that there will be full library support for generator style coroutines in C++23.

The C++20 specification is obviously looking to provide support for parallel (or asynchronous) coroutines using co_await, which makes the implementation of a simpler generator style synchronous coroutines more complex. The implementation requirements for our coroutines utilises a Future and Promise mechanism similar to the std::async mechanism for asynchronous threads.

If you are a Python or C# developer expecting a simple coroutine mechanism, you’ll be disappointed because the C++20 general purpose framework is incomplete. Having said that, there are many blogs and articles on the web that include a template class that supports generator style coroutines. This blog contains a usable coroutine template and example code after discussing what a coroutine is...