clojure.core/realized?

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Type: function Added: Clojure 1.3 Examples: 4 Runnable: 1

([x])

Returns true if a value has been produced for a promise, delay, future or lazy sequence.

Examples

by neotyk on 2012-02-21 . May have evaluation errors. ▶

;; Create a promise (def p (promise)) #'user/p ; p is our promise ;; Check if was delivered/realized (realized? p) false ; No yet ;; Delivering the promise (deliver p 42) #<core$promise$reify__5727@47122d: 42> ;; Check again if it was delivered (realized? p) true ; Yes! ;; Deref to see what has been delivered @p 42 ;; Note that @ is shorthand for deref (deref p) 42

by Dimagog on 2015-02-04 . May have evaluation errors. ▶

;; For lazy sequences (def r (range 5)) #'user/r (realized? r) false (first r) 0 (realized? r) true ; As of Clojure 1.7.0 range may return things other than a LazySeq. ; see https://groups.google.com/forum/#!topic/clojure/NFwHkZxUFuY ; and another example here. (def r (lazy-seq (range 5))) #'user/r (realized? r) false (first r) 0 (realized? r) true

by timrobinson33 on 2021-01-04 ▶

;; Note that for delay (but not future), if the body is currently executing ;; realized? will block until it completes.

by mars0i on 2022-03-03 . May have evaluation errors. ▶

;; realized? does not work with all lazy sequences (since Clojure 1.7.0), ;; and some functions that return lazy sequences might not always return ;; a sequence to which realized? is applicable. ;; realized? works with a bare call to range: (realized? (range)) true (realized? (rest (range))) false ;; but not when range is given an argument: (realized? (range 10000)) Execution error (ClassCastException) at user/eval2036 (form-init1890379966749060098.clj:1). clojure.lang.LongRange cannot be cast to clojure.lang.IPending ;; The reason is that range returns instances of different classes: (class (range)) clojure.lang.Iterate (class (range 10000)) clojure.lang.LongRange ;; repeat is another example: (realized? (repeat 10000)) Execution error (ClassCastException) at user/eval5991 (form-init1890379966749060098.clj:1). clojure.lang.Repeat cannot be cast to clojure.lang.IPending (class (repeat 10000)) clojure.lang.Repeat ;; All of the sequences returned above behave lazily, however. ;; The upshot is that realized? is not considered an important tool for use ;; with lazy sequences and probably shouldn't be depended on, except in ;; special cases. ;; As noted in another example, there's an old discussion here: ;; https://groups.google.com/forum/#!topic/clojure/NFwHkZxUFu

See also

• clojure.core/promise (0)
• clojure.core/delay (3)
• clojure.core/future (1)

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