feature: add branded types

[zkulbeda]

Introduce brand method

const BrandType: unique symbol = Symbol()

interface Brand<K extends string | symbol> {
  readonly [BrandType]: {
    readonly [k in K]: K
  }
}

type Branded<T, K extends string | symbol> = T & Brand<K>

function brand<TSchema extends BaseSchema, const K>(
  schema: TSchema,
  brand: K
): BaseSchema<Input<TSchema>, Branded<Output<TSchema>, K>>{
  return schema
}

const schema = brand(number([maxValue(20)]), "UserId");
parse(schema, 123) // number & Brand<"UserId">

[fabian-hiller]

Can you explain in which specific use cases brand is useful and offers an advantage? I have not quite understood it yet.

[zkulbeda]

Nominal type matching is highly requested typescript feature, and until typescript doesn't have it, branded types is alternative.

See some resources of using them
https://egghead.io/blog/using-branded-types-in-typescript
https://twitter.com/mattpocockuk/status/1625173884885401600

[fabian-hiller]

I think I understand it now. Cool idea. Once I'm done with my bachelor thesis and hopefully have some more time, I can take a closer look at it.

[zkulbeda]

Thanks! I should mention that zod also have brand utility, docs. I think it would simplify migration to valibot. See later great example of implementing nominal types in other lib @effect/data

[fabian-hiller]

If you have time and interest, you can try to implement this feature and submit a PR. I will check your code and give you feedback.

[fabian-hiller]

The brand feature is now available 🎉

[danielo515]

@fabian-hiller if you have finished your degree and you are not yet familiar with this, then you are missing one of the best type safety features and it's a good time for you to investigate it 😁. This exists in several languages with different names, but the same concept:

• ocaml: phantom types
• rust: newtype pattern
• F# constrained types (I think)

Since you seem to be interested in the type safety topic I really recommend taking a look at "domain modeling made functional", for some eye-opening usage examples. For me they are super valuable for IDs (what is that string? A user ID or a car ID?)

[fabian-hiller]

Thank you. I will have a look at it.