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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
44 lines
2.3 KiB
Markdown
44 lines
2.3 KiB
Markdown
# Slice with Lambda — C# demo examples
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Three C# demo examples for the **Slice with Lambda** refactoring.
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Condensed mechanics: https://www.sammancoaching.org/refactorings/slice.html
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(where that page says mock, we use a lambda instead).
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Full Java walkthrough: `../../storyboard/storyboard.md`.
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Slides: `~/qwan/slides-rjs/decks/refactoring/slice-with-lambda/slides.md`, served at http://localhost:9001/#/refactoring/slice-with-lambda.
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## The three examples
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| file | guard (client state) | unwanted dependency | lambda | tail |
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| `MetaphorFree.cs` | `if (a < 0) return 0;` | `_someDependency.mightThrowWhenPreconditionNotSatisfied(a)` | `Func<int, int> readB = a => ...` | `int c = a + b; return c * 2;` |
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| `WeatherStation.cs` | `if (_wateredToday)` | `_lightSensor.Read()` (byte) | `Func<byte> readLight = () => ...` | sunny -> `WateringDuration.Medium`, shady -> `Short` (reading > 128 => `SunExposure.Sunny`) |
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| `IceCreamShop.cs` | `if (_thawedToday)` | `_thermometer.Read()` (byte) | `Func<byte> readTemperature = () => ...` | warm -> `ThawAmount.Medium`, cold -> `Low` (temperature > 25 => `Warmth.Warm`) |
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In all three, the guard reads client state (a parameter or a flag the client
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owns), so it stays in the extracted method. Only the dependency call moves
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into the lambda.
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## The ramp
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`MetaphorFree.cs` is the smallest possible shape: no loop, one dependency
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call, a tail of one arithmetic step. It carries the capture-to-parameter
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lesson: the lambda takes `a` as its parameter (`readB(a)`) because a lambda
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moved up into the function head cannot capture method parameters. Its
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step-4 stub tests include a throwing stub.
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`WeatherStation.cs` and `IceCreamShop.cs` are same-shape domain
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repetitions — guard, one dependency call, map to enum, constant tail — so
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participants can practice extracting the lambda twice. The C# delegate
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syntax (`Func<byte>`) is worth the repetition.
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## Same three regions every time
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Each example deliberately has the same three regions:
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- **before**: guard clauses
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- **middle**: one dependency call
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- **after**: tail that depends on the value the dependency produced
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Matching the pattern: extract the dependency-using code into a lambda,
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slide the definition to the top, extract the method below it, pass the
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lambda as parameter, test with pure lambda stubs. |