store/[org.clojure/clojure "1.8.0"] clj::clojure.core/extenders

Official Documentation

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Arities
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   [protocol]

Docstring
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  Returns a collection of the types explicitly extending protocol

Source

(defn extenders 
  "Returns a collection of the types explicitly extending protocol"
  {:added "1.2"}
  [protocol]
  (keys (:impls protocol)))

Example 1

Edit
(defprotocol P (id [this]))
;; => P

(extend-protocol P 
  String 
  (id [this] this)
  clojure.lang.Symbol 
  (id [this] (name this))
  clojure.lang.Keyword
  (id [this] (name this)))
;; => nil

(extenders P)
;; => (java.lang.String clojure.lang.Symbol clojure.lang.Keyword)

Uses on crossclj