State as a Cookie Jar

What does state have in common with a cookie jar? That's what everybody wants to find out!

Transcript

1. State as a Cookie Jar
   Joy Clark
   

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2. Joy Clark
   Consultant @ innoQ
   joy.clark@innoq.com
   @iamjoyclark
   

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3. View Slide

4. state
   noun
   the particular condition that someone or
   something is in at a specific time.
   @iamjoyclark
   

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5. mutable
   adjective
   liable to change
   @iamjoyclark
   

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6. mutable state
   adjective + noun
   ??
   @iamjoyclark
   

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7. An entity
   changes over
   time…
   @iamjoyclark
   

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8. Character #1
   @iamjoyclark
   

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9. Character #2
   @iamjoyclark
   

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10. Character #3
    @iamjoyclark
    

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11. @iamjoyclark
    Character #4
    

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12. The value changes over time!
    @iamjoyclark
    

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13. Clojure
    (defn take [{cookies ::cookies} to-take]
    (if (< to-take cookies)
    {::cookies (- cookies to-take)}
    {::cookies 0}))
    (defn cookie-monster [cookie-jar to-eat]
    (take cookie-jar to-eat))
    (defn kitten [cookie-jar]
    (take cookie-jar 1))
    (defn grandma [{cookies ::cookies} nr-baked]
    (if (pos? nr-baked)
    {::cookies (+ cookies nr-baked)}
    {::cookies cookies}))
    Joy Clark
    https://github.com/joyclark/cookie-jar
    

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14. Elixir
    defmodule CookieJar do
    defstruct cookies: 0
    def run(%{cookies: cookies}, [:cat | actions]) 

    when cookies > 0 do
    run(%CookieJar{cookies: cookies - 1}, actions)
    end
    def run(_, [:monster | actions]) do
    run(%CookieJar{cookies: 0}, actions)
    end
    def run(%{cookies: cookies}, [:grandma | actions]) do
    run(%CookieJar{cookies: cookies + 1}, actions)
    end
    def run(jar, _), do: jar
    end
    Mario Mainz
    https://github.com/mmainz/cookie_jar
    

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15. Clojure with Mutable State
    (def cookie-jar (atom {::cookies 5}))
    (defn ghost [cookie-jar]
    (take cookie-jar 2))
    (swap! cookie-jar grandma 5)
    (swap! cookie-jar kitten)
    (swap! cookie-jar ghost)
    @cookie-jar // => 7: retrieves current value of cookie-jar
    Joy Clark
    https://github.com/joyclark/cookie-jar @iamjoyclark
    

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16. swap! explained
    @iamjoyclark
    

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17. In an
    otherworldly
    dimension…
    In the kitchen…
    (def cookie-jar
    (atom {::cookies 5}))
    (swap! cookie-jar grandma 5)
    @cookie-jar => {::cookies 8}
    (swap! cookie-jar ghost)
    swap!
    retrieve {::cookies 5}
    (grandma {::cookies 5} 5)
    save! {::cookies 10}
    swap!
    retrieve {::cookies 5}
    (ghost {::cookies 5})
    atom changed, retry!
    retrieve {::cookies 10}
    (ghost {::cookies 10})
    save! {::cookies 8}
    @iamjoyclark
    

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18. That’s All For Now!
    https://github.com/joyclark/cookie-jar
    @iamjoyclark
    

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