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/...

[1]: https://tsplay.dev/N7rvBw

[2]: https://tsplay.dev/Ndep0m