Comment by knome

You can and should put as many as you can there

https://lexi-lambda.github.io/blog/2019/11/05/parse-don-t-va...

If instead of validating that someone has sent you a phone number in one spot and then passing along a string, you can as easily have a function construct an UncheckedPhoneNumber. You can choose to only construct VerifiedPhoneNumbers if the user has gone through a code check. Both would allow you to pluck a PhoneNumber out of them for where you need to have generic calling code.

You can use this sort of pattern to encode anything into the type system. Takes a little more upfront typing than all of those being strings, but your program will be sure of what it actually has at every point. It's pretty nice.