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New in-theme classes: Buyers computes a shopping-list total, PriceList stands for the pricing service (random surge, flaky test). One loop, one lambda-able expression — the third example teaches the move with nothing else in the way. Pristine repo + reference solution (extract lambda, slide, extract method with Func<IceCream,int> parameter, pure-lambda test) + storyboard in the established style. Mirrors the kata's C# setup (net7.0, MSTest); needs a build check on a machine with the SDK.
1.9 KiB
Exercise 3 — Buyers (Split Loop 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 7 — same setup as the kata's csharp/ folder).
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.
Not verified by a build
This exercise was authored without a local .NET SDK (structurally mirrored from
the kata's csharp/ project files). Run dotnet test test/BuyersTests.csproj
once on a machine with the SDK before facilitating.