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javaclojureclojure-java-interop

Get unknown key from Clojure Persistent Hash

What is the best way to get an unknown key from a Clojure map? I tried this - 

(key {:a "test"})

which throws this - 

ClassCastException clojure.lang.PersistenArrayMap cannot be cast to java.util.Map$Entry

Looking at the source code, this makes sense- 

(defn key
  "Returns the key of the map entry."
  {:added "1.0" :static true}
  [^java.util.Map$Entry e]
  (. e (getKey)))

I also tried this- 

(key (java.util.Map$Entry. {:a "test"}))

Which throws this- 

CompilerException java.lang.IllegalArgumentException: No matching ctor found for interface java.util.Map$Entry

I understand that I can call keys and then pull said key from the KeySeq, but I was curious if there is a simple way to do this with one function call.

This is a related question in terms of interop. Thanks for the input.

Solution

  • (key (first {:a "test"})) will get you the key of the first entry in the map, is that what you are trying to do?