# .NET development, ASP.NET Core, C#, Software Architecture, Web Platform APIs, What's new

Published articles for .NET development, ASP.NET Core, C#, Software Architecture, Web Platform APIs, What's new.

This is one page of public article previews, not the complete archive. Follow Next page to continue. Summaries are not the original full articles.

## C# 15 Union Types for API Results: Examples, Trade-Offs, and Migration

DevFeed: [C# 15 Union Types for API Results: Examples, Trade-Offs, and Migration](<https://devfeed.tech/articles/c-15-union-types-for-api-results-examples-trade-offs-and-migration-92884.md>)

Original publisher: [Read original article](<https://www.syncfusion.com/blogs/post/csharp-15-union-types-api-results>)

Author: Arunachalam Kandasamy Raja

Published: 2026-10-21T14:17:46Z

Content type: article

Language: en

Sources: [Syncfusion](<https://devfeed.tech/sources/syncfusion-blogs.md>)

Topics: [union types](<https://devfeed.tech/topics/union-types.md>), [ASP.NET](<https://devfeed.tech/topics/aspnet.md>)

Tags: [api](<https://devfeed.tech/tags/api.md>), [asp-net-core](<https://devfeed.tech/tags/asp-net-core.md>), [business](<https://devfeed.tech/tags/business.md>), [c-sharp](<https://devfeed.tech/tags/c-sharp.md>), [c-sharp-15](<https://devfeed.tech/tags/c-sharp-15.md>), [c-sharp-15-union-types](<https://devfeed.tech/tags/c-sharp-15-union-types.md>), [c-sharp-discriminated-unions](<https://devfeed.tech/tags/c-sharp-discriminated-unions.md>), [c-sharp-result-pattern](<https://devfeed.tech/tags/c-sharp-result-pattern.md>), [c-sharp-union-types](<https://devfeed.tech/tags/c-sharp-union-types.md>), [c-sharp-union-types-in-asp-net-core](<https://devfeed.tech/tags/c-sharp-union-types-in-asp-net-core.md>), [cases](<https://devfeed.tech/tags/cases.md>), [compare](<https://devfeed.tech/tags/compare.md>), [compatibility](<https://devfeed.tech/tags/compatibility.md>), [compilation](<https://devfeed.tech/tags/compilation.md>), [compiler](<https://devfeed.tech/tags/compiler.md>), [examples](<https://devfeed.tech/tags/examples.md>), [microsoft](<https://devfeed.tech/tags/microsoft.md>), [migration](<https://devfeed.tech/tags/migration.md>), [net-11](<https://devfeed.tech/tags/net-11.md>), [net-development](<https://devfeed.tech/tags/net-development.md>), [net-development-asp-net-core-c-sharp-software-architecture-web-platform-apis-what-s-new](<https://devfeed.tech/tags/net-development-asp-net-core-c-sharp-software-architecture-web-platform-apis-what-s-new.md>), [net-sdk](<https://devfeed.tech/tags/net-sdk.md>), [results](<https://devfeed.tech/tags/results.md>), [software-architecture](<https://devfeed.tech/tags/software-architecture.md>), [software-development](<https://devfeed.tech/tags/software-development.md>), [types](<https://devfeed.tech/tags/types.md>), [union](<https://devfeed.tech/tags/union.md>), [union-types](<https://devfeed.tech/tags/union-types.md>), [web-api](<https://devfeed.tech/tags/web-api.md>), [web-platform-apis](<https://devfeed.tech/tags/web-platform-apis.md>), [what-s-new](<https://devfeed.tech/tags/what-s-new.md>)

### AI overview

C# 15 union types represent a fixed set of result cases and let the compiler flag unhandled cases in switch expressions. In the ASP.NET Core example, a service returns distinct order outcomes while a controller maps them to HTTP responses, keeping business logic separate from HTTP handling. Unions suit closed sets of expected outcomes; interfaces better fit extensible implementations, and an established Result<T> may already meet a project's needs. Generated unions store cases through object?, so value types may box; the text recommends measuring performance-sensitive use. JSON deserialization can be ambiguous when structural case shapes overlap, and explicit polymorphic serialization may suit APIs needing a stable discriminator. Because unions are preview features in the C# 15/.NET 11 development cycle, migration guidance is to update internal consumers first and check response contracts, OpenAPI, generated clients, and serialized or persisted data before removing an old result model.

### Source excerpt

Learn how C# 15 union types simplify ASP.NET Core API results, compare with existing C# patterns, and help you decide when to adopt them.