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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.
41 lines
1.9 KiB
Markdown
41 lines
1.9 KiB
Markdown
# Exercise 3 — Buyers (Split Loop with Lambda, the pure rep)
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A third, minimal example in the same kata theme: the sellers exist
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(`DailyForecasts` — Steve, Julie, Francis), the buyers don't. This adds them:
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`Buyers` computes a buyer's shopping-list total, and `PriceList` stands for an
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external pricing service (it adds random surge pricing, so the test is flaky).
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Written in **C#** (MSTest, .NET 7 — same setup as the kata's `csharp/` folder).
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Run with `dotnet test test/BuyersTests.csproj`.
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Contents:
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- `csharp/` — pristine exercise repo: one loop, **one** lambda-able expression
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(`priceList.PriceFor(flavour)`), nothing else. No printing, no conditionals,
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no void calls.
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- `solution/` — end state: extracted static method taking
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`Func<IceCream, int> priceFor`, a no-arg overload passing the method group,
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and a deterministic test with a pure lambda (`_ => 2`).
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`IceCream.cs` is copied from
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[IceCreamForecasting-Refactoring-Kata](https://github.com/emilybache/IceCreamForecasting-Refactoring-Kata)
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(same license as the kata applies).
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## Where this sits in the sequence
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| example | lambda | teaches |
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|---|---|---|
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| 1. `longRangeForecast` weather loop (Java) | `LongFunction<Boolean>` | the pattern + the drift trap |
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| 3. `Buyers` shopping list (C#, this one) | `Func<IceCream, int>` | the move in its purest form: one expression, nothing else |
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| demo/next: `printSalesForecasts` → `SalesScorer`, `PriceList` → `Pricing` | role interface | when one function isn't enough (two side-effectful methods to stub) |
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Next-time arc: marketing adds surge discounts, `PriceList` grows
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`DiscountFor(...)` — two methods to stub → extract a role interface
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(`IPricing`) instead of two lambdas. See the demo script's closing note.
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## Not verified by a build
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This exercise was authored without a local .NET SDK (structurally mirrored from
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the kata's `csharp/` project files). Run `dotnet test test/BuyersTests.csproj`
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once on a machine with the SDK before facilitating.
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