A refined type is simply a subset of a larger type.
Type refinement is the process of converting a large type to a refined type. We use smart constructors to do type refinement.
For example:
- all UUIDs are valid strings, but not all strings are valid UUIDs
- UUIDs are a refined type of
string - the function
makeUuid(input: string): Uuid:- takes a string
- makes sure it contains a valid UUID
- spits out a UUID built from that string
In a business application, many (if not most) of the safe types will actually be refined types.
- Most input data from APIs or web browsers will be converted from strings to the types that form the business domain.
- Same goes for all of the data retrieved from the business's databases.