namespaces - Why IllegalArgumentException "interface is not a protocol" when importing a Clojure protocol?

Question

I followed Cursive's suggestion to Import class when using extend-protocol in a different namespace to the one where defprotocol occurred.

(ns the.first)
(defprotocol AProtocol
  (method [this]))

(ns the.second
  (:import (the.first AProtocol)) ; <= Cursive suggested this...
(extend-protocol AProtocol ; <= ...because this wasn't in scope.
  AType
  (method [this] ...))

I tore my hair out a little at the IllegalArgumentException: interface the.first.AProtocol is not a protocol.

question from:https://stackoverflow.com/questions/66059708/why-illegalargumentexception-interface-is-not-a-protocol-when-importing-a-cloj

Answer 1

Then I realised I should have ignored the IDE's hint, and :required the protocol (and methods, for convenience).

(ns the.second
  (:require [the.first :refer [AProtocol amethod]]))

Only obvious in retrospect.