kijanowski

  // instead of
  public java.util.List<Integer> legacyIterate(Integer... ints) {
    return java.util.Arrays
      .stream(ints)
      .map(i -> i + 1)
      .peek(System.out::println)
      .collect(Collectors.toList());
  }

  // do it the functional way

kijanowski

  // instead of
  public String legacyJoin(String... args) {
    return java.util.Arrays
      .stream(args)
      .collect(Collectors.joining(", "));
  }

  // do it the functional way
  public String vavrJoin(String... args) {
    return io.vavr.collection.List

kijanowski

  // instead of
  public java.util.List<String> legacyIteratingWithIndex1(String... args) {
    java.util.List<String> result = new ArrayList<>();

    for (int i = 0; i < args.length; i++) {
      result.add(i + ". " + args[i]);
    }

    return result;
  }

kijanowski

  // instead of
  public java.util.List<String> legacyFlatMap1(java.util.List<Optional<String>> args) {
    return args
      .stream()
      .filter(Optional::isPresent)
      .map(Optional::get)
      .map(String::toLowerCase)
      .collect(Collectors.toList());
  }

kijanowski

  // instead of
  public Skills legacyFold(java.util.List<String> args) {
    Skills skills = new Skills(args.get(0));
    args.remove(0); // someone may be surprised that passing you a list makes the first element disappearing
    args.forEach(skills::addSkill);
    return skills;
  }

  // do it the functional way
  public Skills vavrFold(io.vavr.collection.Seq<String> args) {

kijanowski

  // instead of
  public java.util.Map legacyJoiningLists1(java.util.List<String> fruits, java.util.List<BigDecimal> priceList) {
    java.util.Map<String, BigDecimal> map = new java.util.HashMap<String, BigDecimal>();
    for (int i = 0; i < fruits.size(); i++) {
      BigDecimal price = i < priceList.size() ? priceList.get(i) : BigDecimal.ZERO;
      map.put(fruits.get(i), price);
    }
    return map;
  }
  // or

kijanowski

  public List<String> flatMapListOfLists(
    List<String> a1, List<String> a2, List<String> a3, List<String> a
  ) {
    List<List<String>> listOfLists = List.of(a1, a2, a3, a4);
    return listOfLists.flatMap(innerList -> innerList);
  }

kijanowski

  public List<String> flatMapListOfListsWithInnerMap(
    List<String> a1, List<String> a2, List<String> a3, List<String> a4
  ) {
    List<List<String>> listOfLists = List.of(a1, a2, a3, a4);
    return listOfLists.flatMap(innerList -> innerList.map(s -> s.toLowerCase()));
  }

kijanowski

  public List<String> flatMapListOfOptions(
    Option<String> a1, Option<String> a2, Option<String> a3
  ) {
    List<Option<String>> b = List.of(a1, a2, a3);
    return b.flatMap(innerOption -> innerOption);
  }

kijanowski

  public List<String> flatMapListOfOptionsWithInnerMap(
    Option<String> a1, Option<String> a2, Option<String> a3
  ) {
    List<Option<String>> b = List.of(a1, a2, a3);
    return b.flatMap(innerOption -> innerOption.map(wrappedString -> wrappedString.toLowerCase()));
  }