[API Proposal]: add regex for pattern matching

[balakhaniyan]

Background and motivation

Hello
Can dotnet team add a feature to pattern matching to use RegEx? (with is keyword)

API Proposal

I think there is no need to submit an API proposal

API Usage

if (data is @"\s+") {

}

Alternative Designs

No response

Risks

No response

[huoyaoyuan]

This is a C# language feature and belongs to https://github.com/dotnet/csharplang/discussions.

Testing IsMatch itself will definitely not be a language feature. It's just a shorthand of one method Regex.IsMatch. This falls under user-defined active pattern, which is discussed at #277 and #4131 .
The more interesting case is to extract the matched captures directly as variables, like the opposite of string interpolation.