[Proposal]: Target-typed inference for type patterns

[MadsTorgersen]

Target-typed inference for type patterns

• Specification: https://github.com/dotnet/csharplang/blob/main/proposals/inference-for-type-patterns.md
• Discussion: [Discussion]: Target-typed inference for type patterns #9631

Summary

Generic type inference is extended to type patterns, which may omit a type argument list when it can be inferred from the pattern input value. For instance, given a declaration Option<int> intOption, instead of:

if (intOption is Some<int> some) ...

You can simply write:

if (intOption is Some some) ... // 'Some<int>' inferred from the type of 'intOption'

Design meetings

• https://github.com/dotnet/csharplang/blob/main/meetings/2025/LDM-2025-08-27.md#type-inference-in-patterns