Protocol functions fail to find future extensions when assigned to a local or new var

Question

`
(defprotocol TestProtocol
(tester [o]))

(let [t tester]
(defn another-tester [o]
(t o)))

(def another-tester2 tester)

(extend-protocol TestProtocol
String
(tester [o] (println "Strings work!")))

(another-tester "A") ;; Error
(another-tester2 "A") ;; Error
(tester "A") ;; Works fine

(let [t tester]
(defn another-tester [o]
(t o)))

(another-tester "A") ;; Works fine

(def another-tester2 tester)

(another-tester2 "A") ;; Works fine

(extend-protocol TestProtocol
Long
(tester [o] (println "Longs work!")))

(another-tester "A") ;; Works fine
(another-tester 3) ;; Error
(another-tester2 3) ;; Error
`

Answer 1

_Comment made by: nathanmarz_

This issue appears to be Clojure specific – I did some testing in CLJS and was unable to reproduce the issue.

Answer 2

Comment made by: gshayban

Nathan,
Not sure if you tried this, but using:

`(def another-handle #'the-protocol-function)`
rather than dereffing outright.

Answer 3

_Comment made by: nathanmarz_

That's a good workaround but it does seem that my test case should work. I ran into this because I was passing around functions dynamically and saving them for later execution – and this issue popped up with protocol methods. Having to pass around protocol methods differently than regular functions doesn't seem right.

Answer 4

Comment made by: hiredman

this is a result of the protocol implementation in clojure, protocol extension mutates the vars, once you have taken then value of the var (which happens once for top level forms) you will not see further mutations of the var so no more protocol extension

Answer 5

Reference: https://clojure.atlassian.net/browse/CLJ-1796 (reported by alex+import)