JavaSlang JavaDayKiev 2016

Transcript

1. Javaslang - Functional Java Done Right Grzegorz Piwowarek gpiwowarek@gmail.com 1
2. Me Dev@TouK Yoyo Player Musician 2
3. pivovarit@ Twitter GitHub ...everywhere else 3
4. pivovarit#2152 4
5. Java 8 5
6. "Functional" Java8: Lambda Expressions Optional, Stream, CompletableFuture ... 6
8. Java 8 issues: Only 3 functional control structures No memoization No lifting No pattern matching No tuples Optional not Serializable/Iterable Lack of Stream/Optional in APIs Checked exceptions in functions "Type pollution" list.stream().map(...).collect(toList()) ... 8
9. List<String> foo(List<String> list); 9
10. List<String> foo(List<String> 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; } 10
11. Potential inputs: declared params instance state global state Potential outputs: declared returned value mutable instance state mutable global state mutable params exceptions 11
12. Potential inputs: declared params Potential outputs: declared returned value 12
13. Functional programming is not about lambdas. 13
14. "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 14
15. Immutability Referential Transparency 15
18. Java Collections API: add() remove() clear() ... 18
19. Date date = new Date(); Set<Date> dates = new HashSet<>(); dates.add(date); date.setTime(42); dates.contains(date); //false 19
21. λ Tuple Value 21
22. λ Function2<Integer, Integer, Integer> sum = (a, b) -> a + b; CheckedFunction2<Integer, Integer, Integer> sum = (a, b) -> a + b; composition lifting currying memoization 22
23. Lifting Function2<Integer, Integer, Integer> divideBy = (a, b) -> a / b; Function2<Integer, Integer, Option<Integer>> lift = lift(divideBy); 23
24. Currying Function2<Integer, Integer, Integer> sum = (a, b) -> a + b; Function1<Int, Function1<Int, Int>> curried = sum.curried(); Function1<Integer, Integer> add2 = curried.apply(2); 24
25. Memoization Function2<Integer, Integer, Integer> sum = (a, b) -> a + b; Function2<Integer, Integer, Integer> memoizedSum = sum.memoized(); 25
26. Function0<Double> mem = Function0.of(Math::random).memoized(); double randomValue1 = memoizedRand.apply(); double randomValue2 = memoizedRand.apply(); then(randomValue1).isEqualTo(randomValue2); 26
27. Tuple Tuple2<String, Integer> java8 = Tuple.of("Java", 8); Tuple2<String, Integer> that = java8.map( s -> s + "slang", i -> i / 4); String transform = java8.transform((s, i) -> s + i); Iterable<?> objects = java8.toSeq() 27
28. Value Option Try Lazy Either Future Validation Collections API public interface Value<T> extends Iterable<T> 28
29. Option 29
30. final String result = Option.of(somethingNullable) .map(Object::toString) .map(String::toLowerCase) .getOrElse(() -> "DEFAULT VALUE"); 30
31. List<Optional<Integer>> list = ... list.stream() .filter(Optional::isPresent) .map(Optional::get) .collect(toList()); List<Option<Integer>> list = ... list.flatMap(o -> o); Java 8 Javaslang 31
32. Try 32
33. Try.of(() -> new URI("bebebe")) .map(URI::getScheme) .getOrElse(() -> "UNKNOWN"); 33
34. Lazy 34
35. Lazy<String> lazy = Lazy.of(this::veryLongComputation) .map(Object::toString) .map(String::toUpperCase); lazy.get(); 35
36. Functional Data Structures 36
37. Functional Data Structures: Persistent Immutable with Referential Transparent methods 37
38. Seq 38
40. public static Stream<Integer> fibonacci() { return Stream.of(1, 1) .appendSelf(self -> self.zip(self.tail()) .map(t -> t._1 + t._2)); } 40
41. Pattern Matching 41
42. String on = Match(i).of( Case(x -> x % 2 == 0, "Even"), Case(x -> x % 2 == 1, "Odd"), Case($(), "?")); Option<String> on = Match(i).option( Case(x -> x % 2 == 0, "Even"), Case(x -> x % 2 == 1, "Odd")); 42
43. String on = Match(i).of( Case($(1), "One"), Case($(2), "Two"), Case($(), "Something else")); 43
44. 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)") ); 44
45. String actual = Match(opt).of( Case(Some($()), String::valueOf), Case(None(), "no value")); 45
46. Match(i).of( Case(is(1), "1"), Case(isIn(2, 3), "2 or 3"), Case(anyOf(is(4), noneOf(is(5), is(6))), "4 or not (5 or 6)"), Case(instanceOf(String.class), "String content"), Case($(), "?") ); http://koziolekweb.pl/2016/06/18/pattern-matching-w-javie-z-javaslang-ii/ 46
47. Match(param).of( Case(isIn("-h", "--help"), o -> run(outerWorld::displayHelp)), Case(isIn("-v", "--version"), o -> run(outerWorld::displayVersion)), Case($(), o -> {})); 47
48. 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); 48
49. www.javaslang.io 49
50. Thank you! gpiwowarek@gmail.com pivovarit@twitter (slides are here!) pivovarit@github 50