# Unions

> Dependency-free C# 15 unions that do not box value-type cases.

The C# 15 `union` keyword lowers to a single `object?` field, so every value-type case is boxed on entry. Purview.Unions generates the language's non-boxing custom-union shape instead: each case gets its own typed field, a public constructor, and a `TryGetValue` that never allocates. The compiler still sees a union — implicit conversions, exhaustive `switch`, and `is`/`null` patterns all work — plus a hand-written `Union<T1, T2>` for the two-case shape.

## Documentation version

- Channel: live (default)
- Source: purview-dev/unions@main

## Resources

- Repository: https://github.com/purview-dev/unions
- NuGet package: https://www.nuget.org/packages/Purview.Unions
- Project page: https://purview.dev/projects/unions/
- Documentation: https://purview.dev/docs/unions/
- Full machine-readable content: https://purview.dev/projects/unions/llms-full.txt

## Documentation pages

- Unions: https://purview.dev/docs/unions/
- Union design: https://purview.dev/docs/unions/union-design/
- Diagnostics: https://purview.dev/docs/unions/diagnostics/
- Interop: https://purview.dev/docs/unions/interop/
- Trimming and Native AOT: https://purview.dev/docs/unions/trimming-aot/
- Performance: https://purview.dev/docs/unions/performance/
- Agent Skills: https://purview.dev/docs/unions/agent-skills/
- Release Flow: https://purview.dev/docs/unions/release-flow/