Javaslang - functional Java done right

Transcript

1. Javaslang - functional Java
   done right
   Grzegorz Piwowarek
   gpiwowarek@gmail.com
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2. Me
   Dev@TouK
   Yoyo Player
   Musician
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3. pivovarit@
   Twitter
   GitHub
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4. pivovarit#2152
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5. Java 8
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6. "Functional" Java8:
   Lambda Expressions
   Optional, Stream, CompletableFuture
   ...
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8. Java 8 issues:
   No functional data structures
   No memoization, no lifting
   No pattern matching
   No Tuple
   Only 3 monadic containers
   Lack of Stream/Optional in APIs
   Checked exceptions in functions
   Type pollution
   list.stream().map(...).collect(toList())
   ...
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9. List foo(List list);
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10. List foo(List list) {
    if (this.state.isEmpty() || list.isEmpty()) {
    throw new IllegalStateException("Ouch...");
    }
    list.add(this.state.get(0));
    list.add(CONSTANT);
    this.moreState.addAll(list);
    OtherClass.mutableStaticField = list;
    return list;
    }
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11. Potential inputs:
    params
    Potential outputs:
    returned value
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12. Potential inputs:
    params
    instance state
    global state
    Potential outputs:
    returned value
    mutable instance state
    mutable global state
    mutable params
    exceptions
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13. Immutability
    Referential
    Transparency
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14. Functional programming is not
    about lambdas.
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15. "Functional programming is about writing pure functions,
    about removing hidden inputs and outputs as far as we can,
    so that as much of our code as possible
    just describes a relationship between inputs and outputs."
    http://blog.jenkster.com/2015/12/what-is-functional-programming.html
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16. Java Collections API:
    add()
    remove()
    clear()
    ...
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17. final Date date = new Date();
    final HashMap map = new HashMap<>();
    map.put(date, "some value");
    date.setTime(123);
    map.containsKey(date); // false
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19. λ
    Tuple
    Value
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20. λ
    Function2 sum = (a, b) -> a + b;
    CheckedFunction2 sum = (a, b) -> a + b;
    composition
    lifting
    currying
    memoization
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21. Lifting
    Function2 divideBy = (a, b) -> a / b;
    Function2> lift = lift(divideBy);
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22. Currying
    Function2 sum = (a, b) -> a + b;
    Function1 add2 = add.curried().apply(2);
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23. Memoization
    Function2 sum = (a, b) -> a + b;
    Function2 memoizedSum = sum.memoized();
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24. Function0 memoizedRand = Function0.of(Math::random).memoized();
    double randomValue1 = memoizedRand.apply();
    double randomValue2 = memoizedRand.apply();
    then(randomValue1).isEqualTo(randomValue2);
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25. Tuple
    Tuple2 java8 = Tuple.of("Java", 8);
    Tuple2 that = java8.map(
    s -> s + "slang",
    i -> i / 4
    );
    String transform = java8.transform((s, i) -> s + i);
    Iterable> objects = java8.toSeq()
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26. Value
    Option
    Try
    Lazy
    Either
    Future
    Validation
    Collections API
    public interface Value extends Iterable
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27. Option
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28. final String result = Option.of(somethingNullable)
    .map(Object::toString)
    .map(String::toLowerCase)
    .getOrElse(() -> "DEFAULT VALUE");
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29. List> list = Arrays
    .asList(Optional.of(1), Optional.empty(), Optional.of(3));
    list.stream()
    .filter(Optional::isPresent)
    .map(Optional::get)
    .collect(toList());
    List list = List.of(Option.of(1), Option.none());
    list.flatMap(o -> o);
    Java 8
    Javaslang
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30. Try
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31. Try.of(() -> new URI("bebebe"))
    .map(URI::getScheme)
    .getOrElse(() -> "UNKNOWN");
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32. Lazy
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33. Lazy lazy = Lazy.of(this::veryLongComputation)
    .map(Object::toString)
    .map(String::toUpperCase);
    lazy.get();
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34. Functional Data
    Structures
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35. Functional Data Structures:
    Persistent
    Immutable
    with Referential Transparent methods
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36. Seq
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38. public static Stream fibonacci() {
    return Stream.of(1, 1)
    .appendSelf(self -> self.zip(self.tail())
    .map(t -> t._1 + t._2));
    }
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39. Pattern Matching
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40. String on = Match(i).of(
    Case(x -> x % 2 == 0, "Even"),
    Case(x -> x % 2 == 1, "Odd"),
    Case($(), "?"));
    Option on = Match(i).option(
    Case(x -> x % 2 == 0, "Even"),
    Case(x -> x % 2 == 1, "Odd"));
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41. String on = Match(i).of(
    Case($(1), "One"),
    Case($(2), "Two"),
    Case($(), "Something else"));
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42. Match(localDate).of(
    Case(LocalDate(2016, 2, 13), () -> "2016-02-13"),
    Case(LocalDate(2016, $(), $_), m -> "month " + m + " in 2016"),
    Case(LocalDate($(2016), $(), $_), (y, m) -> "my" + m + y),
    Case($_, () -> "(catch all)")
    );
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43. Match(i).of(
    Case(is(1), "1"),
    Case(isIn(2, 3), "2 or 3"),
    Case(anyOf(is(4), noneOf(is(5), is(6))), "4 or not (5 or 6)"),
    Case(instanceOf(String.class), "String content"),
    Case($(), "?")
    );
    http://koziolekweb.pl/2016/06/18/pattern-matching-w-javie-z-javaslang-ii/
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44. Try.of(this::doSomething)
    .recover(x -> Match(x).of(
    Case(instanceOf(Exception_1.class), ...),
    Case(instanceOf(Exception_2.class), ...),
    Case(instanceOf(Exception_n.class), ...)
    ))
    .getOrElse(other);
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45. www.javaslang.io
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46. Thank you!
    gpiwowarek@gmail.com
    pivovarit@twitter
    pivovarit@github
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