clojure.core/deref

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Type: function Added: Clojure 1.0 Examples: 3 Runnable: 0

([ref] [ref timeout-ms timeout-val])

Also reader macro: @ref/@agent/@var/@atom/@delay/@future/@promise. Within a transaction, returns the in-transaction-value of ref, else returns the most-recently-committed value of ref. When applied to a var, agent or atom, returns its current state. When applied to a delay, forces it if not already forced. When applied to a future, will block if computation not complete. When applied to a promise, will block until a value is delivered. The variant taking a timeout can be used for blocking references (futures and promises), and will return timeout-val if the timeout (in milliseconds) is reached before a value is available. See also - realized?.

Examples

by dakrone on 2010-07-31 . May have evaluation errors. ▶

(def a (atom 0)) #'user/a @a 0 (deref a) 0 (def b (ref 1)) #'user/b @b 1 (deref b) 1 (def c (agent 2)) #'user/c @c 2 (deref c) 2 (def d (future 3)) #'user/d @d 3 (deref d) 3

by kgann on 2015-01-14 . May have evaluation errors. ▶

(def a (promise)) #'user/a (deref a) ;; blocking until a delivery occurs <ctrl-c> (deref a 100 :timeout) ;; block for at most 100ms :timeout

by viebel on 2018-08-15 . May have evaluation errors. ▶

(def b 1) #'user/b (var b) #'user/b (deref (var b)) 1

See also

• clojure.core/atom (2)
• clojure.core/agent
• clojure.core/ref (1)
• clojure.core/realized? (1)
• clojure.core/future (1)

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