clojure.core/defmethod

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Type: macro Added: Clojure 1.0 Examples: 4 Runnable: 2

([multifn dispatch-val & fn-tail])

Creates and installs a new method of multimethod associated with dispatch-value.

Examples

by Victor on 2010-11-23 ▶

(defmulti service-charge (fn [acct] [(account-level acct) (:tag acct)])) (defmethod service-charge [::acc/Basic ::acc/Checking] [_] 25) (defmethod service-charge [::acc/Basic ::acc/Savings] [_] 10) (defmethod service-charge [::acc/Premium ::acc/Account] [_] 0)

by Victor on 2010-11-23 . May have evaluation errors. ▶

;this example illustrates that the dispatch type ;does not have to be a symbol, but can be anything (in this case, it's a string) (defmulti greeting (fn [x] (get x "language"))) ;params is not used, so we could have used [_] (defmethod greeting "English" [params] "Hello!") (defmethod greeting "French" [params] "Bonjour!") ;then can use this like this: (def english-map {"id" "1", "language" "English"}) (def french-map {"id" "2", "language" "French"}) =>(greeting english-map) "Hello!" =>(greeting french-map) "Bonjour!"

by gstamp on 2011-06-16 . May have evaluation errors. ▶

;; Methods can be given a name. Very useful in stack traces. (defmethod foo "a" name-of-method [params] "was a")

by bfontaine on 2019-10-25 ▶

(defmulti ticket-price :customer-status) (defmethod ticket-price :student ;; Everything after the dispatch value is passed to fn. student-price [customer] 10.0) (defmethod ticket-price :professional professional-price [customer] 650.0)

See also

• clojure.core/defmulti (7)
• clojure.core/remove-method
• clojure.core/remove-all-methods
• clojure.core/prefers
• clojure.core/methods (0)
• clojure.core/get-method

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