package tablecloth-native

Comparator provide a way for custom data structures to be used with Maps and Sets

Say we have a module Book which we want to be able to create a Set of

module Book = struct
  type t = {
    isbn: string;
    title: string;
  }

  let compare bookA bookB =
    String.compare bookA.isbn bookb.isbn
end

First we need to make our module conform to the S signature.

This can be done by using the Make functor.

module Book = struct
  type t = {
    isbn: string;
    title: string;
  }

  let compare bookA bookB =
    String.compare bookA.isbn bookb.isbn
  
  include Comparator.Make(struct 
    type nonrec t = t

    let compare = compare
  end)
end

Now we can create a Set of books

Set.fromList (module Book) [
  { isbn="9788460767923"; title="Moby Dick or The Whale" }
]