clojure.core/delay

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Type: macro Added: Clojure 1.0 Examples: 4 Runnable: 3

([& body])

Takes a body of expressions and yields a Delay object that will invoke the body only the first time it is forced (with force or deref/@), and will cache the result and return it on all subsequent force calls. See also - realized?

Examples

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

;; In this example you can see that the first time the delay is forced ;; the println is executed however the second dereference shows just the ;; precomputed value. (def my-delay (delay (println "did some work") 100)) #'user/my-delay @my-delay did some work 100 @my-delay 100

by jafingerhut on 2014-11-08 ▶

;; Note that the implementation of deref for delays makes it impossible for the ;; body of the delay to be executed more than once, even if the derefs occur ;; from multiple threads near the same time, because it is a synchronized method ;; in Java.

by zk on 2016-08-08 ▶

;; test example

by humorless on 2020-12-01 ▶

;; If you are coming from OOP background, think about a OOP pattern - singleton. ;; delay and singleton can serve the same purpose.

See also

• clojure.core/force (0)
• clojure.core/realized? (1)
• clojure.core/memoize (3)
• clojure.core/future (1)
• clojure.core/delay?

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