Free public beta until December 4, 2026: every course is open, no card needed. After that, the first chapter of each course stays free and full access is a one-time $39 ($19 for up to 100 founding members chosen for helpful feedback). Your progress is kept. How the beta works

runtime type

The class an object was created from with new; it decides which override runs.

The class of the object a reference points to, fixed for the object's lifetime; dynamic dispatch starts its search there.