[Proposal]: Target-typed inference for constructor calls

[MadsTorgersen]

Target-typed inference for constructor calls

• Specification: https://github.com/dotnet/csharplang/blob/main/proposals/inference-for-constructor-calls.md
• Discussion: [Discussion]: Target-typed inference for constructor calls #9629

Summary

Generic type inference is extended to 'new' expressions, which may infer type arguments for the newly created class or struct, including from a target type if present. For instance, given:

public class MyCollection<T> : IEnumerable<T>
{
    public MyCollection() { ... }
    ...
}

We would allow the constructor to be called without a type argument when it can be inferred from arguments or (in this case) a target type:

IEnumerable<string> c = new MyCollection(); // 'T' = 'string' inferred from target type

Design meetings

• https://github.com/dotnet/csharplang/blob/main/meetings/2025/LDM-2025-08-18.md#type-inference
• https://github.com/dotnet/csharplang/blob/main/meetings/2025/LDM-2025-08-20.md#target-type-inference-improvements