clojure.core/longs

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

([xs])

Casts to long[]

Examples

by tomdl89 on 2022-07-01 . May have evaluation errors. ▶

(def my-floats (float-array [1.1 2.2 3.3]));; => #'user/my-floats ;; long-array will convert where possible (long-array my-floats);; => [1, 2, 3] ;; longs will not (try (longs my-floats) (catch ClassCastException e (ex-message e)));; => "[F cannot be cast to [J"

by randomizedthinking on 2023-03-20 . May have evaluation errors. ▶

;; longs does cast but not convert arrays ;; it is used as a type-hinting device to avoid reflections ;; very important for computation intensive codes (binding [*print-meta* true] (def ^longs x (long-array [1 2 4])) (clojure.pprint/pprint #'x)) ;; ^{:tag #function[clojure.core/longs], ...}

by tomdl89 on 2023-04-23 ▶

;; Casting avoids expensive reflection, so to see the benefit, enable warning: (set! *warn-on-reflection* true) ;; We'll def a long-array but won't type-hint the var: (def my-array (long-array [10 20 30 40 50 60])) ;; and try to amap over it without using `longs` or type hinting amap's args: (amap my-array i _ (unchecked-inc ^long (aget my-array i))) ;; Reflection warning… call to static method alength on clojure.lang.RT can't be resolved (argument types: unknown). ;; Reflection warning… call to static method aclone on clojure.lang.RT can't be resolved (argument types: unknown). ;; Reflection warning… call to static method aget on clojure.lang.RT can't be resolved (argument types: unknown, int). ;; Reflection warning… call to static method aset on clojure.lang.RT can't be resolved (argument types: unknown, int, long). ;; => [11, 21, 31, 41, 51, 61] ;; We can use `longs` to avoid reflection: (amap (longs my-array) i _ (unchecked-inc ^long (aget (longs my-array) i))) ;; => [11, 21, 31, 41, 51, 61] ;; Just as we can type hint in place: (amap ^longs my-array i _ (unchecked-inc ^long (aget ^longs my-array i))) ;; => [11, 21, 31, 41, 51, 61] ;; Or type hint the var: (def ^"[J" my-array (long-array [10 20 30 40 50 60])) (amap my-array i _ (unchecked-inc ^long (aget my-array i))) ;; => [11, 21, 31, 41, 51, 61]

See also

• clojure.core/long-array

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