Javaslang - functional Java done right

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1. Javaslang - functional Java done right Grzegorz Piwowarek gpiwowarek@gmail.com 1
2. Me Dev@TouK Yoyo Player Musician 2
3. pivovarit@ Twitter GitHub 3
4. pivovarit#2152 4
5. Java 8 5
6. "Functional" Java8: Lambda Expressions Optional, Stream, CompletableFuture ... 6
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()) ... 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: params Potential outputs: returned value 11
12. Potential inputs: params instance state global state Potential outputs: returned value mutable instance state mutable global state mutable params exceptions 12
13. Immutability Referential Transparency 13
14. Functional programming is not about lambdas. 14
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 15
16. Java Collections API: add() remove() clear() ... 16
17. final Date date = new Date(); final HashMap<Date, Object> map = new HashMap<>(); map.put(date, "some value"); date.setTime(123); map.containsKey(date); // false 17
19. λ Tuple Value 19
20. λ Function2<Integer, Integer, Integer> sum = (a, b) -> a + b; CheckedFunction2<Integer, Integer, Integer> sum = (a, b) -> a + b; composition lifting currying memoization 20
21. Lifting Function2<Integer, Integer, Integer> divideBy = (a, b) -> a / b; Function2<Integer, Integer, Option<Integer>> lift = lift(divideBy); 21
22. Currying Function2<Integer, Integer, Integer> sum = (a, b) -> a + b; Function1<Integer, Integer> add2 = add.curried().apply(2); 22
23. Memoization Function2<Integer, Integer, Integer> sum = (a, b) -> a + b; Function2<Integer, Integer, Integer> memoizedSum = sum.memoized(); 23
24. Function0<Double> memoizedRand = Function0.of(Math::random).memoized(); double randomValue1 = memoizedRand.apply(); double randomValue2 = memoizedRand.apply(); then(randomValue1).isEqualTo(randomValue2); 24
25. 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() 25
26. Value Option Try Lazy Either Future Validation Collections API public interface Value<T> extends Iterable<T> 26
27. Option 27
28. final String result = Option.of(somethingNullable) .map(Object::toString) .map(String::toLowerCase) .getOrElse(() -> "DEFAULT VALUE"); 28
29. List<Optional<Integer>> list = Arrays .asList(Optional.of(1), Optional.empty(), Optional.of(3)); list.stream() .filter(Optional::isPresent) .map(Optional::get) .collect(toList()); List<Integer> list = List.of(Option.of(1), Option.<Integer>none()); list.flatMap(o -> o); Java 8 Javaslang 29
30. Try 30
31. Try.of(() -> new URI("bebebe")) .map(URI::getScheme) .getOrElse(() -> "UNKNOWN"); 31
32. Lazy 32
33. Lazy<String> lazy = Lazy.of(this::veryLongComputation) .map(Object::toString) .map(String::toUpperCase); lazy.get(); 33
34. Functional Data Structures 34
35. Functional Data Structures: Persistent Immutable with Referential Transparent methods 35
36. Seq 36
38. public static Stream<Integer> fibonacci() { return Stream.of(1, 1) .appendSelf(self -> self.zip(self.tail()) .map(t -> t._1 + t._2)); } 38
39. Pattern Matching 39
40. String on = Match(i).of( Case(x -> x % 2 == 0, "Even"), Case(x -> x % 2 == 1, "Odd"), Case($(), "?")); Option<String> on = Match(i).option( Case(x -> x % 2 == 0, "Even"), Case(x -> x % 2 == 1, "Odd")); 40
41. String on = Match(i).of( Case($(1), "One"), Case($(2), "Two"), Case($(), "Something else")); 41
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)") ); 42
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/ 43
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); 44
45. www.javaslang.io 45
46. Thank you! gpiwowarek@gmail.com pivovarit@twitter pivovarit@github 46