Comment by matt_kantor
4 hours ago
EDIT: previously the example in the parent comment was:
type NewType<T> = T & { __brand__ : Symbol }
---
This seems wrong; the type spelled `Symbol` refers to the boxed interface for symbols[0]. I suspect you meant to write `unique symbol` there, but it can't be used in that position.
I'm not sure if `NewType` in your comment is supposed to stand in for a specific newtype (in which case it probably doesn't need to be generic[1]) or if it's supposed to be a general-purpose type constructor for any newtype (in which case it should take a second type parameter to let me distinguish e.g. `EmailAddress` from `Password`[2]). The use of `unique symbol`s is also only really necessary if you want to keep the brand private to force users to go through a validation function or whatnot, otherwise you can just use string literal types.
I agree these incantations aren't big problems (it all falls out naturally from knowledge of TypeScript's type system, and can be abstracted away as per my comment in [2]), but the fact that you goofed in the very comment where you were trying to make that point is causing me to second-guess myself.
[0]: https://github.com/microsoft/TypeScript/blob/v6.0.3/src/lib/...
Right. Besides getting this incantation right, as gp did only after editing their comment, you also have to cast to create values of NewType. But generally you want to avoid casting in typescript if you care about type safety, so now everybody has to remember the rule that in this particular circumstance it's the right thing to do.
There are helper libraries to ease this (zod supports branded types, I think?), but I guess my general point is that while typescript might give you the ingredients you need to implement type safety in cases like this if you try really hard and remember all your rules everywhere, it doesn't come naturally so it's hard to maintain at scale.
Yeah we just use Zod’s branded type and that pretty much handles it. No casts, use a refinement then slap a brand on it.
I was on the Tube and wanted to get my reply in before entering a tunnel. I already corrected it whilst I was underground.
I think the point still stands - is this really a big problem? I guess I couldn't recite the syntax from memory, because I usually use a utility type for this