Question

Suppose I have a bunch of Clojure data structures, all of the same type – for example an object type defined by defrecord.

What is the best way to get polymorphic behaviour across these structures?

Would it be good practice to embed a function within the structure so that I can do something like:

((:my-method my-object) param1 param2)

Or is there a better way?

Answer 1

You can use multimethods for dispatch,

(derive ::subtype ::type)

then you can dispatch based on type

(defmulti my-method
  (fn [type] ((meta type) :type)))

(defmethod my-method ::subtype []
  ;;stuff...
 )

You need to add :type to the objects metadata when you create it,

(with-meta [1 2 3] {:type ::subtype})

or I haven’t tried this but since protocols and records creates java classes behind the scenes you dispatch based on that name.