ClassCastException MyType cannot be cast to MyType?

Question

I have encountered a problem when using deftype in Clojure. If I run the following code:

(defprotocol TestProt
  (geta [this])
  (getb [this]))

(deftype TestType [a b]
  TestProt
  (geta [this] a)
  (getb [this] b))

(defn test-function [^TestType a-testtype]
  (print (.geta a-testtype))) 

(def test-tt (TestType. 1 1))

(test-function test-tt)

Then the compiler throws: ClassCastException MyProject.core.TestType cannot be cast to MyProject.core.TestType. Am I doing something wrong, or is this a bug? Note that if I remove the type annotation from test-function, so it's just:

(defn test-function [a-testtype]
  (print (.geta a-testtype))) 

Then the code works fine, but I get a warning (with warn-on-reflect enabled) about reflection, and it runs slower, which defeats the purpose of using deftype in my current use-case.

Edit: Okay, the code works in the repl, but not when I load it using ctrl-alt-s (I'm running it in Eclipse via Counterclockwise). So the problem seems to be with Eclipse or Counterclockwise.

Answer 1

This kind of thing happens when you redefine a type (with deftype or defrecord) but somewhere there's a use of the previously existing class hanging around, in your case in the type hint.

I couldn't reproduce the behavior you describe with CountercClockwise's CtrlAltS, but it does appear evaluating the following expressions in a fresh REPL, so it might somehow help to diagnose your specific situation.

(defprotocol TestProt
  (geta [this])
  (getb [this]))

(deftype TestType [a b]
  TestProt
  (geta [this] a)
  (getb [this] b))

(defn test-function [^TestType a-testtype]
  (print (.geta a-testtype)))

(def test-tt (TestType. 1 1))

(println :first (test-function test-tt))

;= :first 1

;; redefine the type...
(deftype TestType [a b]
  TestProt
  (geta [this] a)
  (getb [this] b))

;; ...and the test-tt var with the new version     
(def test-tt (TestType. 1 1))

(println :second (test-function test-tt))

;= ClassCastException user.TestType cannot be cast to user.TestType  user/test-function (NO_SOURCE_FILE:89)