How to dispatch multimethod on primitive types?

Question

I want my program act differently between primitive types and their wrapper classes, for example:

(defmulti try-type class)

(defmethod try-type Integer [arg]
  (println "Integer"))

(defmethod try-type Integer/TYPE [arg]
  (println "int"))

But it doesn't work, though i try Integer and int both

user=> (try-type (.intValue (int 2)))
Integer
nil
user=> (try-type  (int 2))
Integer
nil

So, is it possible to dispatch multimethod on primitive types?

======EDIT======

i was wrapping a google guava into clojure. There is a primitive library in it, such as Booleans, Dobules, Ints etc. They have some methods in common, so i want to try multimethod.

could you explain why you want to do this? currently dispatching on primitives is not possible, but there is probably a good way to achieve the same objective (google "XY Problem") — mikera, Jul 30 '12 at 00:46

score 4 · Answer 1 · answered Jul 28 '12 at 18:38

No, it is not currently possible. An arg to a function (such as the multimethod dispatch function) is either an Object (thus primitives will be boxed) or a primitive long/double (thus Objects will be unboxed). Your scenario requires a function that can take either and preserve that distinction inside the function.

That said, there may be solutions to whatever is the actual problem you're trying to solve.

How to dispatch multimethod on primitive types?

1 Answers1