How would you convert a Number type to a ClampedNumber type without casting?

Ah, yeah you’re right. I somehow thought typescript could do type narrowing based on checks - like say:

If (i >= 1) { // i’s type now includes >= 1 }

But that is not the case, so you’d need a single cast to make it work (from number to ClampedNumber<1,200>) or however exactly you’d want to express this.

Tbf having looked more closely into how typescript handles number range types, I don’t think I would ever use them. Not very expressive or clear. I think I hallucinated something closer to what is in this proposal: https://github.com/microsoft/TypeScript/issues/43505

I still think that the general idea of communicating what acceptable input is via the type system is a good one. But the specifics of doing that with numbers isn’t great in typescript yet.

How would you implement it in other languages that support it better? Can you literally just do a range check and the compiler infers its range for types? If so thats actually pretty neat.

What about documentation as in docstring, function signature label and the like. I quite like CommonLisp, EmacsLisp, Go for that.

Yeah, that’s probably the best possible implementation outside of the type system. The issue with docstrings is that they aren’t checked. So you’ve communicated the api to the coder, and maybe even to the ide, but not to the compiler.