CLJ-1831 Add map-entry? predicate

Signed-off-by: Stuart Halloway <stu@cognitect.com>

Author: puredanger

src/clj/clojure/core.clj

@@ -1425,6 +1425,15 @@
 
 ;;map stuff
 
+(defn map-entry?
+  "Return true if x is a map entry"
+  {:added "1.8"}
+  [x]
+  (and (instance? java.util.Map$Entry x)
+    (if (instance? clojure.lang.IPersistentVector x)
+      (= 2 (count x))
+      true)))
+
 (defn contains?
   "Returns true if key is present in the given collection, otherwise
   returns false.  Note that for numerically indexed collections like

src/clj/clojure/core_deftype.clj

@@ -132,7 +132,7 @@
 (defn- imap-cons
   [^IPersistentMap this o]
   (cond
-   (instance? java.util.Map$Entry o)
+   (map-entry? o)
      (let [^java.util.Map$Entry pair o]
        (.assoc this (.getKey pair) (.getValue pair)))
    (instance? clojure.lang.IPersistentVector o)

src/clj/clojure/inspector.clj

@@ -21,7 +21,7 @@
 
 (defn collection-tag [x]
   (cond 
-   (instance? java.util.Map$Entry x) :entry
+   (map-entry? x) :entry
    (instance? java.util.Map x) :seqable
    (instance? java.util.Set x) :seqable
    (sequential? x) :seq

test/clojure/test_clojure/data_structures.clj

@@ -704,6 +704,16 @@
          ai3 ao3
          ai4 ao4)))
 
+(deftest test-map-entry?
+  (testing "map-entry? = false"
+    (are [entry]
+      (false? (map-entry? entry))
+      nil 5 #{1 2} '(1 2) {:a 1} [] [0] [1 2 3]))
+  (testing "map-entry? = true"
+    (are [entry]
+      (true? (map-entry? entry))
+      [1 2] (first (doto (java.util.HashMap.) (.put "x" 1))))))
+
 ;; *** Sets ***
 
 (deftest test-hash-set