clojure.core/empty

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Type: function Added: Clojure 1.0 Examples: 3 Runnable: 1

([coll])

Returns an empty collection of the same category as coll, or nil

Examples

by gstamp on 2010-07-28 . May have evaluation errors. ▶

(empty '(1 2)) ;; => () (empty [1 2]) ;; => [] (empty {1 2}) ;; => {} (empty #{1 2}) ;; => #{} ;; Works for PersistentQueue as well, which is slightly harder to see (def q (conj clojure.lang.PersistentQueue/EMPTY 1)) ;; => #'user/q q ;; => #<PersistentQueue clojure.lang.PersistentQueue@20> (seq q) ;; => (1) (def empty-q (empty q)) ;; => #'user/empty-q empty-q ;; => #<PersistentQueue clojure.lang.PersistentQueue@1> (seq empty-q) ;; => nil ;; returns nil when input is not supported or not a collection (empty (int-array [1 2])) ;; => nil (empty 1) ;; => nil (map empty [[\a \b] {1 2} (range 4)]) ;; => ([] {} ()) (swap! (atom (range 10)) empty) ;; => ()

by TimMc on 2012-10-09 . May have evaluation errors. ▶

;; The output will not necessarily be of the same JVM class as the input (class (seq [1])) clojure.lang.PersistentVector$ChunkedSeq (class (empty (seq [1]))) clojure.lang.PersistentList$EmptyList

by kwladyka on 2015-08-04 ▶

;; Create the same data structure with the same metadata, but empty (def foo (with-meta #{1 2 3} {:some-meta 1})) foo ;; => #{1 2 3} (meta foo) ;; => {:some-meta 1} (def empty-foo (empty foo)) empty-foo ;; => #{} (meta empty-foo) ;; => {:some-meta 1}

See also

• clojure.core/not-empty (4)
• clojure.core/empty? (5)

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