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The refactoring is now published as Slice on sammancoaching.org: https://sammancoaching.org/refactorings/slice.html - git mv ideas/split-loop-with-lambda -> ideas/slice-with-lambda - rename learning-hour file and update frontmatter name - update paths in tools/rehearse scripts and report title - update prose: 'Split Loop with Lambda' -> 'Slice with Lambda' in learning hour, exercise READMEs, storyboard, solution comments - link the published Slice refactoring from the pattern draft
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Exercise 3 — Buyers (Slice with Lambda, the pure rep)
A third, minimal example in the same kata theme: the sellers exist
(DailyForecasts — Steve, Julie, Francis), the buyers don't. This adds them:
Buyers computes a buyer's shopping-list total, and PriceList stands for an
external pricing service (it adds random surge pricing, so the test is flaky).
Written in C# (MSTest, .NET 10; verified with dotnet test on SDK
10.0.4xx — pristine test is flaky by design, solution is deterministic).
Run with dotnet test test/BuyersTests.csproj.
Contents:
csharp/— pristine exercise repo: one loop, one lambda-able expression (priceList.PriceFor(flavour)), nothing else. No printing, no conditionals, no void calls.solution/— end state: extracted static method takingFunc<IceCream, int> priceFor, a no-arg overload passing the method group, and a deterministic test with a pure lambda (_ => 2).
IceCream.cs is copied from
IceCreamForecasting-Refactoring-Kata
(same license as the kata applies).
Where this sits in the sequence
| example | lambda | teaches |
|---|---|---|
1. longRangeForecast weather loop (Java) |
LongFunction<Boolean> |
the pattern + the drift trap |
3. Buyers shopping list (C#, this one) |
Func<IceCream, int> |
the move in its purest form: one expression, nothing else |
demo/next: printSalesForecasts → SalesScorer, PriceList → Pricing |
role interface | when one function isn't enough (two side-effectful methods to stub) |
Next-time arc: marketing adds surge discounts, PriceList grows
DiscountFor(...) — two methods to stub → extract a role interface
(IPricing) instead of two lambdas. See the demo script's closing note.
Verified
Built and run with dotnet test (SDK 10.0.4xx): solution green deterministically,
pristine test flaky (failed 2 of 3 runs, passed 1 — both surges rolled 0).
MSTest bumped to 3.6.4 (kata ships 2.1.1, whose transitive Newtonsoft.Json trips
a NU1903 vulnerability warning).