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doc source examples comments

1.3.0 permalink

1.2.0
1.3.0

defonce

clojure.core

(defonce name expr)

defs name to have the root value of the expr iff the named var has no root value,
else expr is unevaluated

1 Example top

link | changes
```
user> (defonce foo 5)
#'user/foo

user> foo
5

;; defonce does nothing the second time
user> (defonce foo 10)
nil

user> foo
5
```
user> (defonce foo 5) #'user/foo user> foo 5 ;; defonce does nothing the second time user> (defonce foo 10) nil user> foo 5

Source clojure/core.clj:5124 top

(defmacro defonce
  "defs name to have the root value of the expr iff the named var has no root value,
  else expr is unevaluated"
  {:added "1.0"}
  [name expr]
  `(let [v# (def ~name)]
     (when-not (.hasRoot v#)
       (def ~name ~expr))))

Vars in clojure.core/defonce:

Used in 0 other vars

ClojureDocs(beta)

Clojure Core

Namespaces

defonce

clojure.core

1 Example top

See Also top

Source clojure/core.clj:5124 top

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