Community Post: C# 15 union types and closed hierarchies - #26207
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Co-authored-by: Cursor <cursoragent@cursor.com>
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fahrigedik
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Copilot review overview
🟡 Changes recommended
Unresolved review findings include a critical architectural issue and an ambiguity in the reusable generic result example.
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Review effort: Lite
Findings: 1
Open (3)
What changed in this PR
This PR adds a Community Article on C# 15 union types, closed hierarchies, and ABP integration.
Changes:
- Explains exhaustive state and result modeling.
- Covers JSON serialization, caching, and versioning.
- Provides API, generic-result, and migration guidance.
| File | Review summary |
|---|---|
docs/en/Community-Articles/2026-09-23-csharp-15-union-types-and-closed-hierarchies/post.md |
Open findings cover a critical layering issue, generic-result conversion ambiguity, sample reproducibility, and closed-hierarchy wording. |
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| Placing an order has four *expected* outcomes, and only one of them is a success. Running out of stock isn't exceptional in an online shop; it happens every day, and the caller must handle it. That's a perfect fit for the `PlaceOrderResult` union we declared earlier. The domain service returns cases directly, and the implicit conversion works even through `Task<PlaceOrderResult>`: | ||
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| ```csharp | ||
| public async Task<PlaceOrderResult> PlaceAsync(PlaceOrderInput input, CancellationToken cancellationToken = default) |
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| public static implicit operator Result<T>(T value) => new Success<T>(value); | ||
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| public static implicit operator Result<T>(Error error) => new Failure<T>(error); |
| dotnet add test/OrderDemo.Tests package Microsoft.Extensions.TimeProvider.Testing | ||
| ``` | ||
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| Then add the code from this article: the domain types, `Order`, `OrderPlacementService`, the in-memory stores, the API's `Program.cs` and DTOs, and the `Directory.Build.props` from the migration section. The API also needs `public partial class Program;` at the end of `Program.cs`, so that `WebApplicationFactory<Program>` can find it. |
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