learning-hour-maker/ideas/slice-with-lambda/exercise/solution/README.md

Reference solution — end state after step 3

Derived from IceCreamForecasting-Refactoring-Kata (same license as the kata applies to the copied IceCream.java).

Run with mvn test — the approval test passes deterministically without touching the weather service.

What changed vs the exercise start

1. Weather loop extracted to collectExpectedWeather(LongFunction<Boolean>) — a static method whose only "unwanted dependency" is the lambda parameter.
2. Public no-arg longRangeForecast() delegates to a new overload that takes the weather function, keeping existing callers working.
3. Test passes a pure lambda (daysForward -> true) — the original test called the no-arg method and was flaky because of Scorer's Random.

Variations to try (for the debrief or a second round)

• daysForward -> false (no sunny holidays): scores drop to +10 only.
• daysForward -> daysForward == 5 (exactly one sunny holiday, and it is not expectedWeather.get(1), so no +2): all flavours 10.
• Delete the scorer.updateSelection() call inside the production lambda: the approved file does not change — the forecast never reads Scorer.flavour.
• Variation end state: skip the overload; make collectExpectedWeather package-private and test it directly with pure lambdas. Trade-off: tests the pure slice but not the composition (scoring loop).