Multimethods

defmulti.clj

(ns amazing-defmulti)

(defmulti needs-food
  (fn [person] (:is-hungry person)))
(defmethod needs-food true [person] "This person needs food.")
(defmethod needs-food false [person] "This person is well fed.")
(def steve {:is-hungry true})
(def joe {:is-hungry false})

(defn needs-food-if [person]
  (if (:is-hungry person)
    "This person needs food."
	"This person is well fed."))

#_(= (needs-food steve) "This person needs food.")
#_(= (needs-food joe) "This person is well fed.")
(= (needs-food-if steve) "This person needs food.")
(= (needs-food-if joe) "This person is well fed.")

(defmulti attack
  (fn [my-character]
    (:class my-character)))
	
(defmethod attack :barbarian [my-character] (str (:name my-character) " swings his axe for lethal blow."))
(defmethod attack :mage [my-character] (str (:name my-character) " waves the wand and unleashes fall of heavy bricks from the nether."))
	
#_(attack {:class :barbarian :name "Patrick"})
(attack {:class :mage :name "Aaron"})

A great cheatsheet!

If the multimethod only takes one parameter and only uses a keyword to get a value from a map, we can just use the keyword directly as the dispatch function:

(defmulti needs-food :is-hungry)
(defmulti attack :class)

A great cheatsheet!

If the multimethod only takes one parameter and only uses a keyword to get a value from a map, we can just use the keyword directly as the dispatch function:

(defmulti needs-food :is-hungry)
(defmulti attack :class)

Yes! So efficient! 😊