clojure.core/set-validator!

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Type: function Added: Clojure 1.0 Examples: 2 Runnable: 0

([iref validator-fn])

Sets the validator-fn for a var/ref/agent/atom. validator-fn must be nil or a side-effect-free fn of one argument, which will be passed the intended new state on any state change. If the new state is unacceptable, the validator-fn should return false or throw an exception. If the current state (root value if var) is not acceptable to the new validator, an exception will be thrown and the validator will not be changed.

Examples

by nickbauman on 2012-01-18 . May have evaluation errors. ▶

(def atm (atom [2])) #'user/atm (set-validator! atm #(every? even? %)) nil (swap! atm into [5]) #<CompilerException java.lang.IllegalStateException: Invalid reference state (NO_SOURCE_FILE:0)> (set-validator! atm nil) nil (swap! atm into [5])) [2 5]

by beoliver on 2017-10-29 . May have evaluation errors. ▶

(def a 1) #'user/a (set-validator! (var a) (fn [update-result] (< update-result 3))) nil (alter-var-root (var a) inc) 2 (alter-var-root (var a) inc) IllegalStateException Invalid reference state clojure.lang.ARef.validate (ARef.java:33) a 2

Note by TimMc

If you want your validator to throw an exception with a useful message, make sure it is a RuntimeException (or subclass), otherwise ARef#validate will throw an IllegalStateException with a generic message.

See also

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

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