That's neat, I was about to ask which languages support that since the vast majority don't. I didn't know that you can do that in Typescript.

Any language with an type system really...

Even OOP : if you have a string class, you can have a String_Formated_For_API subtype.

Just extends String, and add some checking.

But now the type checker "knows" it can print() a String_Formated_For_API just fine but not call_API(string).