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Code RoomForce unwrap crashes on nil
MediumPrep Room Coding #4205

Force unwrap crashes on nil

Vibe & agenticAlgorithms & data structuresMid–Senior~14 min

An AI wrote this Swift code to parse a price from an API response and format it for display in a checkout cell. It passes the dev's manual test, but you get a spike of crash reports in production from a single screen. What's the bug and how would you catch it before shipping?

Implement
display_price(field_lines: list[str], supported_currencies: list[str]) → str
Examples
in[["amount_cents=1299","currency=USD"],["USD","EUR"]]out"USD 12.99"
in[["currency=USD"],["USD","EUR"]]out"unavailable"
in[["amount_cents=5","currency=EUR"],["USD","EUR"]]out"EUR 0.05"
What a strong answer looks like

Treat the AI’s output as a draft to verify, not an answer to trust. Name the specific flaw and the input that triggers it, say how you’d catch it (tests, edge cases, reading critically), and how you’d re-prompt or decompose to get it right.

0:00 of about 14 min

Vibe & agentic: describe the solution in plain language (or narrate it) and the coach grades your approach.

Which questions mattered is sealed until you submit. Telling you now would just be handing over the edge cases.