The only difference between F# and C# with respect to the notion of a "type which represents a string of length 15" is the amount of code to do it - as describe

The only difference between F# and C# with respect to the notion of a "type which represents a string of length 15" is the amount of code to do it - as described by Scott Wlaschin [1]. You could do the equivalent in C# too. I don't know if this is also the case in Ocaml, though. [1]: https://fsharpforfunandprofit.com/posts/designing-with-types-more-semantic-types/#modeling-constrained-strings-with-types https://fsharpforfunandprofit.com/posts/designing-with-types...