Create optional fields on Clojure record?

Question

When I instantiate a clojure record I get an error if I do not set all the fields of the record. How can I specify some of the fields to be optional?

Answer 1

defrecord declares a type and a constructor, but the type implements the clojure map interface. You just need to put the required fields in the declaration. For example,

(defrecord MyRecord [required1 required2])

(defn make-my-record [r1 r2 & [opt1 opt2]]
  (assoc (MyRecord. r1 r2) :optional1 opt1 :optional2 opt2))

Can be used like,

user> (make-my-record 1 2)
#:user.MyRecord{:required1 1, :required2 2, :optional2 nil, :optional1 nil}
user> (make-my-record 1 2 :a :b)
#:user.MyRecord{:required1 1, :required2 2, :optional2 :b, :optional1 :a}