clojure.core/identical?

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Type: function Added: Clojure 1.0 Examples: 7 Runnable: 3

([x y])

Tests if 2 arguments are the same object

Examples

by dpritchett on 2010-07-14 . May have evaluation errors. ▶

(def x 1) #'user/x (identical? x x) true (identical? x 1) true (identical? x 2) false (identical? x ((constantly 1) 8)) true (identical? 'a 'a) false

by jafingerhut on 2012-02-22 . May have evaluation errors. ▶

(def x {:foo 1, :bar -3}) #'user/x (def y {:foo 1, :bar -3}) #'user/y ;; Values are equal, but different objects were constructed (= x y) true (identical? x y) false

by MPechorin on 2015-05-09 ▶

; Java wrapper class caching ; details at: https://www.owasp.org/index.php/Java_gotchas#Immutable_Objects_.2F_Wrapper_Class_Caching (identical? 128 128) false (identical? 127 127) true (identical? -127 -127) true (identical? -128 -128) true (identical? -130 -130) false

by ertugrulcetin on 2016-08-11 . May have evaluation errors. ▶

(def a (String. "abc")) ;;=> #'user/a (def b (String. "abc")) ;;=> #'user/b => (identical? a b) ;;=> false ;; initialised 2 new objects (def a "abc") ;;=> #'user/a (def b "abc") ;;=> #'user/b => (identical? a b) ;;=> true ;; refers same objects(address), look String pooling

by wontheone1 on 2019-04-29 . May have evaluation errors. ▶

;; two keywords with the same value are the same object (= :abc :abc) => true (identical? :abc :abc) => true ;; two symbols with the same name are different objects (= 'abc 'abc) => true (identical? 'abc 'abc) => false ;; Strings are interned. see https://en.wikipedia.org/wiki/String_interning (= "abc" "abc") => true (identical? "abc" "abc") => true

by reborg on 2020-01-07 ▶

;; When there is no interning (1000 is outside long range ;; of automatically interned numbers), autoboxing plays ;; interesting tricks: (let [x 1000 y x] (identical? x y)) ;; false ;; This is practically equivalent to the following, ;; which explains what is going on during Clojure evaluation: (let [x 1000 y x] (identical? (Long/valueOf x) (Long/valueOf y))) ;; false

by jafingerhut on 2020-10-26 ▶

;; In general, other examples where `identical?` returns true are ;; often implementation-specific optimizations that can change from one ;; JDK version to another, or one version of Clojure to another. ;; You should think _very_ carefully before writing code that relies on ;; `identical?` returning true. ;; One scenario where it is safe to use `identical?` can be seen in the ;; implementation of Clojure's function `get-in`, where a sentinel object ;; is freshly constructed, and thus guaranteed to be not identical? to any ;; other object that existed before the function was called. This new ;; object is used as a default value in case a lookup of a key in a map fails ;; to find a matching key. Regardless of what values the map contains, it is ;; guaranteed that if the return value is `identical?` to this freshly allocated ;; sentinel object, it could not have been found in the map.

See also

• clojure.core/= (4)
• clojure.core/== (5)

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