[Proposal]: Pattern-based with-expressions

[MadsTorgersen]

Pattern-based with-expressions

• Specification: Not created. See below.
• Discussion: Champion "pattern-based `with` expressions" #8876

Summary

In C# 9.0, we did with on records only, not some generalized pattern-based with expression.

See also

• the proposal in https://github.com/dotnet/csharplang/blob/main/proposals/rejected/records.md for one possible approach.
• Discussion of nested use cases in Discussion: complex nested `with` expressions #77

Design meetings

https://github.com/dotnet/csharplang/blob/main/meetings/2022/LDM-2022-09-26.md#construction-improvements