defprotocol – Clojure docs and tutorials

Want some Object Oriented Programming in Clojure? Here’s a quick example.

Let’s create a dog object.

(ns temp2020toss.dogo)

(defprotocol Bark
  "Just a protocol"
  (barking [this] "bark")
  (hungry [this] "hangry")
  (sleeping[this] "zzzz"))

(defrecord Dog [breed ^Integer age color]
  Bark
  (barking [this] (str "barking my breed ... " (:breed this)))
  (hungry [this] (str "I'm so hungry I could age one whole year to ... " (str (inc (:age this)))))
  (sleeping [this] (str "Really tired, and it has nothing to do with my fur color that is " (:color this)))
  )

(ns temp2020toss.dogo)

(defprotocol Bark

"Just a protocol"

(barking [this] "bark")

(hungry [this] "hangry")

(sleeping[this] "zzzz"))

(defrecord Dog [breed ^Integer age color]

Bark

(barking [this] (str "barking my breed ... " (:breed this)))

(hungry [this] (str "I'm so hungry I could age one whole year to ... " (str (inc (:age this)))))

(sleeping [this] (str "Really tired, and it has nothing to do with my fur color that is " (:color this)))

)

Now let’s use the dog object.

(ns temp2020toss.core
  (:gen-class)
  (:require [temp2020toss.dogo]
            [temp2020toss.dogo :refer :all])
  (:import (temp2020toss.dogo Dog)))

(defn -main
  "I don't do a whole lot ... yet."
  [& args]
  (println "Hello, World!")

  (let [my-dog (Dog. "chow" 8 "green")]
    (println "-->" (:breed my-dog))
    (println "-->" (barking my-dog))))

(ns temp2020toss.core

(:gen-class)

(:require [temp2020toss.dogo]

[temp2020toss.dogo :refer :all])

(:import (temp2020toss.dogo Dog)))

(defn -main

"I don't do a whole lot ... yet."

[& args]

(println "Hello, World!")

(let [my-dog (Dog. "chow" 8 "green")]

(println "-->" (:breed my-dog))

(println "-->" (barking my-dog))))

See, OOP in Clojure is fairly simple. This sample uses protocols with records, but you can add polymorphism with just a little extra work. For polymorphism, use records and multimethods.

I absolutely love the user razvan’s Clojure defrecord example over at stackoverflow, so I copied it here. I know I’ll never find it again if I don’t. Look at the original over on stackoverflow at this link.

Here’s the example …

Clojure defrecord example:

;;define Address record
(defrecord Address [city state])

;;define Person record
(defrecord Person [firstname lastname ^Address address])

;;buid the constructor
(defn make-person ([fname lname city state]
    (->Person fname lname (->Address city state))))

;;create a person
(def person1 (make-person "John" "Doe" "LA" "CA"))

;;retrieve values
(:firstname person1)
(:city (:address person1))

;;define Address record

(defrecord Address [city state])

;;define Person record

(defrecord Person [firstname lastname ^Address address])

;;buid the constructor

(defn make-person ([fname lname city state]

(->Person fname lname (->Address city state))))

;;create a person

(def person1 (make-person "John" "Doe" "LA" "CA"))

;;retrieve values

(:firstname person1)

(:city (:address person1))

If you’re looking for more information on combining protocols with records in Clojure, then Matthew Boston has the blog for you!

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Copyright 2020 T Gene Davis

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Tag: defprotocol

Quick OOP Example

Razvan’s ‘defrecord’ Example