Add split-loop-with-lambda learning hour: draft, pre-factored exercise, solution

- Samman learning hour: 5/5/10/25/5 outline; pairs stop at extracted method taking the lambda as a parameter - exercise/java: pre-factored variant of the kata (Q1/Q4 dead branch stripped, dates as constant), approval test red/flaky by design - exercise/solution: collectExpectedWeather(LongFunction<Boolean>) + no-arg overload; deterministic approval test (all-sunny lambda) - rehearse-with-agent.md: rehearsal setup with qwen + java-refactoring-mcp
2026-09-27 13:30:00 +00:00
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+# Exercise folder — Split Loop with Lambda (learning hour)
+
+Contents:
+
+- `java/` — pre-factored exercise repo (prefactored-longrange; runs with `mvn test`)
+- `solution/` — reference end state after step 3 (extracted method taking the lambda)
+- `rehearse-with-agent.md` — how Willem rehearses this with qwen-code + java-refactoring-mcp
+
+## Reference solution
+
+See `solution/`. End state of the production code (simplified):
+
+```java
+public Map<IceCream, Integer> longRangeForecast() {
+    return longRangeForecast(daysForward -> {
+        scorer.updateSelection();
+        return scorer.lookupWeather(daysForward);
+    });
+}
+
+public Map<IceCream, Integer> longRangeForecast(
+        LongFunction<Boolean> dayOffsetToWeather) {
+    var expectedWeather = collectExpectedWeather(dayOffsetToWeather);
+    // ... reset loop + scoring loop, unchanged ...
+}
+
+private static List<Boolean> collectExpectedWeather(
+        LongFunction<Boolean> dayOffsetToWeather) {
+    var expectedWeather = new ArrayList<Boolean>();
+    for (Instant interestingDate : DATES) {
+        long daysForward = ChronoUnit.DAYS.between(ANCHOR_DATE, interestingDate);
+        expectedWeather.add(dayOffsetToWeather.apply(daysForward));
+    }
+    return expectedWeather;
+}
+```
+
+Notes on the end state:
+
+- Key move: `scorer` is used **only inside the lambda**; the extracted method
+  `collectExpectedWeather` has no dependency on `Scorer` at all — all its
+  inputs are parameters.
+- The public no-arg overload keeps callers unchanged; it injects the
+  "real" weather lambda. The test calls the overload with a pure
+  `daysForward -> true` instead.
+- The test is pure and glanceable: `alwaysSunny` weather gives
+  `{Strawberry:12, Chocolate:12, Vanilla:17, }` (approved file included).
+- `scorer.updateSelection()` turned out to be deletable (it only mutates
+  static `Scorer.flavour` state that this method never reads). Leaving it
+  in the lambda is fine for step 3; deleting it is a debrief aha.