Dependency management in Clojure

Dependencies between components are one of the primary drivers of the flexibility of any bigger applications. Clojure provides a number of tools to manage dependencies, some are built-in, some are built on libraries. We’ll look at basic building blocks like higher-order functions and protocols, but also at libraries like Stuart Sierra’s component.

Presentation by Holger Schauer at ClojureD, Berlin, 2016-02-20

Transcript

1. View Slide

2. View Slide

3. View Slide

4. View Slide

5. View Slide

6. View Slide

7. (ns playitloud.ui-player
   (:require [playitloud.simple-player :refer [play]]))
   (defn play-pressed [randomize]
   (println "User pressed play")
   (play randomize))
   

   View Slide

8. (ns playitloud.ui-player
   (:require [playitloud.simple-player :refer [play]]))
   (defn play-pressed [randomize]
   (println "User pressed play")
   (play randomize))
   (ns playitloud.simple-player
   (:require [playitloud.speaker :refer [blare]]
   [playitloud.musiccoll :refer [get-songs]]))
   (defn play [randomize]
   (let [songs (get-songs)
   songs (if randomize (shuffle songs) songs)]
   (map (fn [song]
   (blare song))
   songs)))
   

   View Slide

9. (ns playitloud.ui-player
   (:require [playitloud.simple-player :refer [play]]))
   (defn play-pressed [randomize]
   (println "User pressed play")
   (play randomize))
   (ns playitloud.simple-player
   (:require [playitloud.speaker :refer [blare]]
   [playitloud.musiccoll :refer [get-songs]]))
   (defn play [randomize]
   (let [songs (get-songs)
   songs (if randomize (shuffle songs) songs)]
   (map (fn [song]
   (blare song))
   songs)))
   (ns playitloud.speaker)
   (defn blare [song]
   (let [result (str "Speaker plays " song)]
   (println result)
   result))
   

   View Slide

10. View Slide

11. (ns playitloud.ho.player)
    (defn play [blarefn songgetterfn randomize]
    (let [songs (songgetterfn)
    songs (if randomize (shuffle songs) songs)]
    (map (fn [song]
    (blarefn song))
    songs)))
    

    View Slide

12. (ns playitloud.ho.player)
    (defn play [blarefn songgetterfn randomize]
    (let [songs (songgetterfn)
    songs (if randomize (shuffle songs) songs)]
    (map (fn [song]
    (blarefn song))
    songs)))
    ; ---------------------------------------------------
    (ns playitloud.ho.ui-player
    (:require [playitloud.ho.player :as ho :refer [play]]
    [playitloud.speaker :as speaker]
    [playitloud.headphone :as headphone]
    [playitloud.blue-streamer :as streamer]
    [playitloud.musiccoll :refer [get-songs]]))
    (defn play-pressed [speaker randomize]
    (println "User pressed play")
    (condp = speaker
    :speaker (play speaker/blare get-songs randomize)
    :headphone (play headphone/blare get-songs randomize)
    :stream (play streamer/blare get-songs randomize)))
    

    View Slide

13. (defn make-playfn
    "Returns a function that will play all songs"
    [blarefn songgetterfn]
    (fn ; Plays all songs, potentially randomized
    [randomize]
    (let [songs (songgetterfn)
    songs (if randomize (shuffle songs) songs)]
    (map (fn [song]
    (blarefn song))
    songs))))
    

    View Slide

14. (ns playitloud.ho.play-config [...]
    (def speaker-play (make-playfn speaker/blare get-songs))
    (def headphone-play (make-playfn headphone/blare get-songs))
    (def stream-play (make-playfn streamer/blare get-songs))
    (defn select-playfn [speaker]
    (condp = speaker
    :speaker speaker-play
    :headphone headphone-play
    :stream stream-play))
    (ns playitloud.ho.clos-ui-player
    (:require [playitloud.ho.play-config :refer [select-playfn]]))
    (defn play-pressed [output randomize]
    (let [playfn (select-playfn output)]
    (playfn randomize)))
    

    View Slide

15. (ns playitloud.services.config)
    (def ^:dynamic *services*
    {:blare playitloud.speaker/blare
    :get-songs playitloud.musiccoll/get-songs})
    

    View Slide

16. (ns playitloud.services.config)
    (def ^:dynamic *services*
    {:blare playitloud.speaker/blare
    :get-songs playitloud.musiccoll/get-songs})
    (ns playitloud.services.player
    (:require [playitloud.services.config :refer [*services*]]))
    (defn- blare [sound]
    ((:blare *services*) sound))
    (defn- get-songs []
    ((:get-songs *services*)))
    

    View Slide

17. (ns playitloud.services.config)
    (def ^:dynamic *services*
    {:blare playitloud.speaker/blare
    :get-songs playitloud.musiccoll/get-songs})
    (ns playitloud.services.player
    (:require [playitloud.services.config :refer [*services*]]))
    (defn- blare [sound]
    ((:blare *services*) sound))
    (defn- get-songs []
    ((:get-songs *services*)))
    (defn play [randomize]
    (let [songs (get-songs)
    songs (if randomize (shuffle songs) songs)]
    (map (fn [song]
    (blare song))
    songs)))
    

    View Slide

18. (ns playitloud.sig.output-device
    (:require [de.find-method.funsig :refer [defsig]]))
    (defsig blare "Play sound loudly!" [sound])
    

    View Slide

19. (ns playitloud.sig.output-device
    (:require [de.find-method.funsig :refer [defsig]]))
    (defsig blare "Play sound loudly!" [sound])
    (ns playitloud.sig.speaker
    (:require [de.find-method.funsig :refer [defimpl]]
    [playitloud.sig.output-device :refer [blare]]))
    (defimpl blare [sound]
    (let [result (str "Speaker plays " sound)]
    (println result)
    result))
    

    View Slide

20. (ns playitloud.sig.output-device
    (:require [de.find-method.funsig :refer [defsig]]))
    (defsig blare "Play sound loudly!" [sound])
    (ns playitloud.sig.speaker
    (:require [de.find-method.funsig :refer [defimpl]]
    [playitloud.sig.output-device :refer [blare]]))
    (defimpl blare [sound]
    (let [result (str "Speaker plays " sound)]
    (println result)
    result))
    (ns playitloud.sig.player
    (:require [playitloud.sig.output-device :refer [blare]]
    [playitloud.musiccoll :as mc :refer [get-songs]]))
    (defn play [randomize]
    (let [songs (get-songs)
    songs (if randomize (shuffle songs) songs)]
    (map (fn [song]
    (blare song))
    songs)))
    

    View Slide

21. (ns playitloud.proto.output-device)
    (defprotocol OutputDevice
    (blare [device sound])
    (inc-volume [device])
    (dec-volume [device]))
    (ns playitloud.proto.speaker
    (:require [playitloud.proto.output-device
    :as output :refer :all]))
    (defrecord Speaker [volume]
    OutputDevice
    (blare [_ sound]
    (let [result (str "Speaker plays " sound)]
    (println result)
    result))
    ;[...]
    

    View Slide

22. (ns playitloud.proto.player
    (:require [playitloud.proto.output-device :as output]
    [playitloud.musiccoll :as mc]))
    (defn play [output-device randomize]
    (let [songs (mc/get-songs)
    songs (if randomize (shuffle songs) songs)]
    (map (fn [song]
    (output/blare output-device song))
    songs)))
    

    View Slide

23. View Slide

24. View Slide

25. View Slide

26. View Slide

27. with-...
    

    View Slide

28. with-...
    binding map
    

    View Slide

29. View Slide

30. (ns playitloud.comp.streamer
    (:require [com.stuartsierra.component :as component]
    [playitloud.comp.output-device :as output :refer :all]
    [playitloud.comp.remote-connection :as remote]))
    (defrecord BlueStreamer [connection volume]
    OutputDevice
    (blare [streamer sound]
    ;... normal protocol/record implementation ...)
    component/Lifecycle
    (start [streamer]
    (println "BlueStreamer starting")
    (connect (:connection streamer) streamer)
    (assoc streamer :status :connected))
    (stop [streamer]
    (println "BlueStreamer stopping")
    (disconnect (:connection streamer) streamer)
    (->> (assoc streamer :status :disconnected)
    (dissoc :connection))))
    (defn new-blue-streamer [config]
    (->BlueStreamer nil (:default-volume config)))
    

    View Slide

31. (ns playitloud.comp.config
    (:require [com.stuartsierra.component :as component]
    [playitloud.comp.blue-connection :as blueconn]
    [playitloud.comp.streamer :as streamer]
    [playitloud.comp.player :as player]))
    (def default-config
    {:bt-conn {:name "Fabuluous-Connectivity" :port "1234"}
    :default-volume 5})
    (defn make-player-system
    "Setup the player system"
    ([]
    (make-player-system default-config))
    ([config]
    (component/system-map
    :connection (blueconn/new-connection config)
    :output-device (component/using
    (streamer/new-blue-streamer config)
    [:connection])
    :player (component/using
    (player/new-player)
    [:output-device]))))
    

    View Slide

32. fun-a
    A
    fun-b fun-a
    A
    B
    B A
    

    View Slide

33. View Slide

34. View Slide

35. View Slide

36. View Slide

37. View Slide