How to add LanguagePrimitives.GenericZero / get_Zero to System.String?

Question

Note: I added a lot of Of interest comments at the end. These are not mean to suggest that one should use inline and static type parameters

Answer 1

Extension members aren't considered as part of member constraint resolution, so you're out of luck. With constraints that involve more than one type (such as the constraint on (+)), you can work around this via the use of a second type, but for the constraint on GenericZero there's no good workaround.