clojure.core/hash

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

([x])

Returns the hash code of its argument. Note this is the hash code consistent with =, and thus is different than .hashCode for Integer, Short, Byte and Clojure collections.

Examples

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

(hash "a") 1455541201 (.hashCode "a") ; notice that this is different than (hash "a") 97 (hash 1) 1392991556 (.hashCode 1) ; notice that this is different than (hash 1) 1 (hash nil) 0 (hash [1 2 3]) 30817 (hash [1 2 3 4]) 955331

by jafingerhut on 2019-01-26 ▶

;; In most cases, hash is _consistent_ with =, meaning that for two values x, y, ;; if (= x y), then (= (hash x) (hash y)). This is a property of hash that ;; is relied upon for hash-based lookup of keys in maps and ;; elements in sets to work correctly. ;; There are some pairs of Java objects x, y where even though (= x y) is true, ;; (= (hash x) (hash y)) is _not_ true. ;; Search for the word "consistent" in this article for some categories of such ;; objects: https://clojure.org/guides/equality ;; In particular, the section titled "Equality and hash": ;; https://clojure.org/guides/equality#equality_and_hash

by loeschzwerg on 2022-03-15 . May have evaluation errors. ▶

;; Equality is measured by the content ;; Hashes of lists AND vectors are equal by content => (= (hash '(1 2 3)) (hash [1 2 3])) true ;; Also works with clojure-"Objects" like LazySeq => (= (hash [1 2 3]) (hash (map identity [1 2 3]))) true ;; but not with sets => (= (hash [1 2 3]) (hash (set [1 2 3]))) false

Note by svenschoenung

Despite what the doc-string says values returned by (hash) are different from (.hashCode) for more than just Integer, Short, Byte and Clojure collections.

The list also includes: Keywords, Symbols, Functions, Sequences, String, Long and BigInteger (as of Clojure 1.7.0).

See also

• clojure.core/get (8)
• clojure.core/hash-ordered-coll (0)
• clojure.core/hash-unordered-coll (0)

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