Coroutines (C++20 Overview)

A coroutine is a function that can suspend and later resume exactly where it left off — C++20's co_await/co_yield/co_return keywords opt a function into this, but (unlike some languages) the standard library ships almost no ready-made coroutine types of its own; using them well typically means either a library (like cppcoro) or writing your own supporting types.

// Conceptual shape only — a real generator needs a supporting
// "promise type" beyond the scope of this overview lesson.
Generator<int> countUpTo(int n) {
    for (int i = 0; i < n; i++) {
        co_yield i; // suspend here, producing i, resuming on next request
    }
}

This lesson deliberately stays at the conceptual level — coroutines are one of C++20's most powerful but least beginner-friendly features, and are worth a dedicated deep dive once the rest of modern C++ feels solid.