>encoding that a number is between 2 and 200

What’s the point of this level of autism when you still have to add run time checks?

For a function setVelocity() that can accept 1..<200. You call it with numbers that you enter directly and types tell you something that would otherwise be a comment on the function, or you do runtime checks elsewhere, and the type becomes proof that you checked them before handing it into the function.

Btw, using “autism” to mean “pedantry” leaves a bit of a bad taste in my mouth. Maybe you could reconsider using it that way in the future.

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samdoesnothing 5 hours ago | parent [-]

Pushing everything to types like this creates a different burden where you're casting between types all over the place just to use the same underlying data. You could just clamp velocity to 200 in the callee and save all that hassle.

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kennywinker 4 hours ago | parent [-]

Casting? Not really - i think you’d only need a couple type checks.

Imo this is mostly useful for situations where you want to handle input validation (and errors) in the UI code and this function lives far away from ui code.

Your point about clamping makes sense, and it’s probably worth doing that anyway, but without it being encoded in the type you have to communicate how the function is intended to be used some other way.

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samdoesnothing 3 hours ago | parent [-]

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

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kennywinker 2 hours ago | parent [-]

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.

	▲	samdoesnothing 2 hours ago \| parent [-]
		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.