Newsubtypes in TS

newsubtype.ts

type Tag = { readonly __tag: symbol }
export type NewSubtype<Base, Tagg extends Tag> = Base & Tagg;
export type NewSubtypeCompanion<T extends NewSubtype<E, Tagg>, E = any, Tagg extends Tag = any> = {
    create: (_: E) => NewSubtype<T, Tagg>
}
export const createNewtypeCompanion: <T extends NewSubtype<E, Tagg>, E = any, Tagg extends Tag = any>() => NewSubtypeCompanion<T, E> =
    <T extends NewSubtype<E, Tagg>, E, Tagg extends Tag>() => ({
        create: (x: E) => x as NewSubtype<T, Tagg>
    })


type A = NewSubtype<number, { readonly __tag: unique symbol }>
const A: NewSubtypeCompanion<A> = createNewtypeCompanion()

type B = NewSubtype<number, { readonly __tag: unique symbol }>
const B: NewSubtypeCompanion<B> = createNewtypeCompanion<B>()

const f1 = (_: A) => null
const f2 = (_: number) => null
const b: B = B.create(2)

f1(b) // doesnt compile
f2(b)