performance

Acceptance measures the hardware and production measures the whole system, so the gap lives in everything acceptance did not cover. Four candidate layers, the order to eliminate them, and the two that account for most of these cases.

The standard forces one heap allocation per entry and a pointer dereference per lookup, and that is a specification requirement rather than a library weakness. The measured cost on this machine, the open-addressing layout that removes it, and the two cases where the standard container is still the right pick.

A speedup number with no method behind it is worth nothing, and experienced interviewers stop listening at the number and start asking about the baseline. What makes a performance claim survive scrutiny, and the four ways a real one turns out to be smaller than it looked.