Clojure's Reference Types

Transcript

1. 1.

   NATE SMITH @nwjsmith theinternate.com

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   Clojure's REFERENCE TYPES

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   ATOMS AGENTS REFS

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   VARS

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   (def wayne-gretzky {:number 99 :position "C" :goals 45}) wayne-gretzky ;;

   => {:number 99 :position "C" :goals 45}
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   wayne_gretzky = { number: 99, position: "C", goals: 45 }

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   (def wayne-gretzky {:number 99 :position "C" :goals 45}) (defn score

   [player] (update-in player [:goals] inc))
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   wayne-gretzky ;; => {:number 99 :position "C" :goals 45} (score

   wayne-gretzky) ;; => {:number 99 :position "C" :goals 46}
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   wayne-gretzky ;; => {:number 99 :position "C" :goals 45} (score

   wayne-gretzky) ;; => {:number 99 :position "C" :goals 46} wayne-gretzky ;; => {:number 99 :position "C" :goals 45}
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    IDENTITY and STATE

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    None
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    None
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    None
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    None
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    IDENTITY ≠ STATE

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    None
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    None
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    BOTH MICHAEL JACKSON

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    WHAT CHANGED?

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    HIS IDENTITY

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    STATE IS IMMUTABLE, IDENTITIES CHANGE

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    wayne_gretzky = { number: 99, position: "C", goals: 45 }

    wayne_gretzky[:goals] += 1 wayne_gretzky # => { number: 99, position: "C", goals: 46 }
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    ATOMS AGENTS REFS

24. 24.

    ATOMS

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    (def atomic-wayne-gretzky (atom {:position "C" :number 99 :goals 0})) (deref

    atomic-wayne-gretzky) ;; => {:position "C" :number 99 :goals 0} @atomic-wayne-gretzky ;; => {:position "C" :number 99 :goals 0}
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    (def atomic-wayne-gretzky (atom {:position "C" :number 99 :goals 0})) (dothreads!

    (fn [] (swap! atomic-wayne-gretzky score)) :threads 100 :times 100) @atomic-wayne-gretzky ;; => {:position "C" :number 99 :goals 10000}
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    AGENTS

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    (def agent-gretzky (agent {:position "C" :number 99 :goals 0})) @agent-gretzky

    ;; => {:position "C" :number 99 :goals 0}
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    (defn score-slowly [player] (Thread/sleep 5000) (update-in player [:goals] inc)) (send

    agent-gretzky score-slowly) @agent-gretzky ;; => {:position "C" :number 99 :goals 0} @agent-gretzky ;; => {:position "C" :number 99 :goals 0} ;; 5 seconds later... @agent-gretzky ;; => {:position "C" :number 99 :goals 1}
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    REFS

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    THEY'RE FRIGGIN' MAGIC

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    (def gretzky-curr (ref {:position "C" :number 99 :goals 0})) (def

    gretzky-prev (ref @gretzky-curr)) @gretzky-curr ;; => {:position "C" :number 99 :goals 0} @gretzky-prev ;; => {:position "C" :number 99 :goals 0}
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    (dothreads! (fn [] (dosync (ref-set gretzky-prev @gretzky-curr) (alter gretzky-curr score)))

    :threads 100 :times 100) @gretzky-prev ;; => {:position "C" :number 99 :goals 9999} @gretzky-curr ;; => {:position "C" :number 99 :goals 10000}
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    Atoms: independent, synchronous Agents: independent, asynchronous Refs: coordinated, synchronous

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    THANKS!

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    None