Coroutines

Coroutines are functions that can suspend and resume their execution while keeping their state. The evolution of functions goes in C++ one step further. Coroutines are with high probability part of C++20.

What I present in this section as a new idea in C++20 is quite old. The term coroutine was coined by Melvin Conway. He used it in his publication on compiler construction in 1963. Donald Knuth called procedures a special case of coroutines. Sometimes, it just takes a while to get your ideas accepted.

With the new keywords co_await and co_yield, C++20 extends the execution of C++ functions with two new concepts.

Thanks to co_await expression it is possible to suspend and resume the execution of the expression. If you use co_await expression in a function func, the call auto getResult = func() does not block if the result of the function is not available. Instead of resource-consuming blocking, you have resource-friendly waiting.

co_yield expression allows it to write a...