Skip to content
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

observable behaviour

What a program does that the outside world can see - its output, files and volatile accesses. The optimizer must keep it; everything else may change.

Observable behaviour is the sequence of volatile accesses, the data written to files at termination, and interactive I/O; it is the only thing the as-if rule obliges an optimized program to preserve.

See also

as-if rule optimization pass
Read the full section →