Create constructor

As discussed in the previous section, a branded type is a way to add a unique label to a primitive type, ensuring that values of different branded types are not interchangeable.

.type<brand, primitive>

In Unwrap, you create branded type using the .type generic. For example,

import { Brand } from `@unnullable/unwrap`

type UserId = Brand.type<"UserId", string>
type ProductId = Brand.type<"ProductId", string>

In the example above the UserId and ProductId are the brands for the corresponding string primitives. You can assign these values by casting:

const userId = "6" as UserId
const productId = "66" as ProductId

Now you can't swap userId with productId as they represent two different brands even though they have the same underlying primitive.

.create<brandedType>()

Type casting is fine, but you can also use .create to create a type constructor:

const UserId = Brand.create<UserId>()
const ProductId = Brand.create<ProductId>()

const userId = UserId(6)
const productId = ProductId(66)

This approach is especially useful when you need to create multiple instances of UserId throughout your codebase.

In the next section, we introduce the .define method, which allows you to embed business logic into the created types, adding custom validation or transformation logic.