Can I add fields to clojure types?

clojure, deftype, types

Solution

Actually you can treat types as maps, you just need to extend clojure.lang.IPersistentMap (an implementation is magically supplied).

(deftype A [a b]
  clojure.lang.IPersistentMap)
(A 1 2) ;; => #:A{:a 1, :b 2}
(assoc (A 1 2) :c 3) ;; => #:A{:a 1, :b 2, :c 3}

Note

Clojure has since split the semantics of types into `defrecord` and `deftype`. For most application-level programming, you'll want to use records. Conveniently, they automatically provide an implementation of `clojure.lang.IPersistentMap`, no magic necessary.

Problem

Clojure structs can be arbitrarily extended, adding new fields. Is it possible to extend types (created using deftype) in a similar way? EDIT: For the benefit future visitors, as Brian pointed out below, this feature is subject to change.

Original source