clojure.core/gensym

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Type: function Added: Clojure 1.0 Examples: 4 Runnable: 1

([] [prefix-string])

Returns a new symbol with a unique name. If a prefix string is supplied, the name is prefix# where # is some unique number. If prefix is not supplied, the prefix is 'G__'.

Examples

by devn on 2010-08-02 . May have evaluation errors. ▶

(gensym "foo") foo2020 (gensym "foo") foo2027 (gensym "foo") ;; ...

by devn on 2010-08-02 . May have evaluation errors. ▶

(gensym) G__2034 (let [my-unique-sym (gensym)] my-unique-sym) G__2075

by gdavis on 2014-03-07 . May have evaluation errors. ▶

;; syntax-reader uses gensym for non-namespace-qualified symbols ending with '#' ;; http://clojure.org/reader `(name0#) ; gensym, form is useful in defmacro (name0__1206__auto__) `(user/name1#) ; no gensym, namespace-qualified (user/name1#) `(:key0#) ; no gensym, keyword (:key0#) `(::key1#) ; no gensym, keyword (:user/key1#)

by tomdl89 on 2022-06-30 ▶

;; syntax-reader gensyms are only generated once, at read time ;; so recursive macros get the same generated symbol for all levels of recursion (defmacro reader-gensym-macro [[x & more :as xs] acc] (if (seq xs) `(let [x# ~x] (reader-gensym-macro ~more (conj ~acc x#))) acc)) (reader-gensym-macro [1 2] []) ;; => [2 2] ;; using the function `gensym` can overcome this problem ;; so recursive macros get a different generated symbol for each level of recursion (defmacro function-gensym-macro [[x & more :as xs] acc] (if (seq xs) (let [gx (gensym 'x)] `(let [~gx ~x] (function-gensym-macro ~more (conj ~acc ~gx)))) acc)) (function-gensym-macro [1 2] []) ;; => [1 2]

Note by mlb

The

(. clojure.lang.RT (nextID))

present gensym's source code (https://github.com/clojure/clojure/blob/clojure-1.5.1/src/jvm/clojure/lang/RT.java#L468) uses java.util.concurrent.atomic.AtomicInteger (and has for the past 6 years, if you trust the Git history).

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