Funktionen, Collections und Records

int addiere(int a, int b) => a + b;                 // Pfeilsyntax für Einzeiler

String gruss(String name, {String anrede = 'Hallo', int? alter}) {      // benannte Parameter
  var text = '$anrede, $name!';
  if (alter != null) text += ' ($alter)';
  return text;
}

int summe(List<int> zahlen, [int start = 0]) {       // optionale Positionsparameter
  var s = start;
  for (final z in zahlen) { s += z; }
  return s;
}

(int, int) minMax(List<int> liste) {                 // Record als Rückgabe (Dart 3)
  return (liste.reduce((a, b) => a < b ? a : b), liste.reduce((a, b) => a > b ? a : b));
}

int fakultaet(int n) => n <= 1 ? 1 : n * fakultaet(n - 1);

Function(int) addierer(int n) => (x) => x + n;       // Closure als Rückgabewert

void main() {
  print(addiere(2, 3));
  print(gruss('Mia'));
  print(gruss('Tom', anrede: 'Hi', alter: 25));
  print(summe([1, 2, 3]));
  print(summe([1, 2, 3], 10));
  final (kleinster, groesster) = minMax([4, 9, 1, 7]);
  print('$kleinster $groesster');
  print(fakultaet(10));
  var plus5 = addierer(5);
  print(plus5(10));

  var verdopple = (int x) => x * 2;                  // anonyme Funktion
  print([1, 2, 3].map(verdopple).toList());
  print([1, 2, 3].map((e) => e * e).toList());
}

5
Hallo, Mia!
Hi, Tom! (25)
6
16
1 9
3628800
15
[2, 4, 6]
[1, 4, 9]

void main() {
  var f = ['Apfel', 'Birne', 'Kirsche'];
  f.add('Dattel');
  f.insert(0, 'Ananas');
  f.remove('Birne');
  print('$f ${f.length} ${f.first} ${f.last} ${f[1]} ${f.indexOf('Kirsche')}');
  print('${f.contains('Apfel')} ${f.sublist(1, 3)} ${f.reversed.toList()} ${f.join(', ')}');
  var z = [5, 3, 9, 1, 7];
  z.sort();
  print(z);
  z.sort((a, b) => b.compareTo(a));
  print(z);
  print('${z.reduce((a, b) => a + b)} ${z.fold(0, (s, x) => s + x)} ${z.where((x) => x > 4).toList()}');
  print('${z.map((x) => x * 2).toList()} ${z.any((x) => x > 8)} ${z.every((x) => x > 0)}');
  print('${z.take(2).toList()} ${z.skip(3).toList()} ${z.firstWhere((x) => x < 6)} ${z.indexWhere((x) => x == 3)}');
  var mehr = [...z, 100];                             // Spread-Operator
  var bedingt = [1, if (z.isNotEmpty) 2, for (var i in [3, 4]) i * 10];   // collection if/for
  print('$mehr $bedingt');
  var matrix = [[1, 2], [3, 4]];
  print('${matrix[1][0]} ${matrix.expand((r) => r).toList()}');
  var festeListe = List<int>.filled(3, 0);
  var generiert = List.generate(5, (i) => i * i);
  print('$festeListe $generiert');
  var unveraenderlich = List.unmodifiable([1, 2, 3]);
  try { unveraenderlich.add(4); } catch (e) { print('Fehler: ${e.runtimeType}'); }
}

[Ananas, Apfel, Kirsche, Dattel] 4 Ananas Dattel Apfel 2
true [Apfel, Kirsche] [Dattel, Kirsche, Apfel, Ananas] Ananas, Apfel, Kirsche, Dattel
[1, 3, 5, 7, 9]
[9, 7, 5, 3, 1]
25 25 [9, 7, 5]
[18, 14, 10, 6, 2] true true
[9, 7] [3, 1] 5 3
[9, 7, 5, 3, 1, 100] [1, 2, 30, 40]
3 [1, 2, 3, 4]
[0, 0, 0] [0, 1, 4, 9, 16]
Fehler: UnsupportedError

void main() {
  var alter = {'Mia': 17, 'Tom': 25};
  alter['Zoe'] = 31;
  alter.putIfAbsent('Ben', () => 9);
  alter.remove('Tom');
  print('${alter['Mia']} ${alter['Nix']} ${alter.length} ${alter.containsKey('Zoe')}');
  alter.forEach((k, v) => print('$k => $v'));          // Einfügereihenfolge bleibt erhalten
  print('${alter.keys.toList()} ${alter.values.toList()}');
  print(alter.map((k, v) => MapEntry(k.toUpperCase(), v + 1)));
  print(Map.fromEntries(alter.entries.where((e) => e.value > 10)));

  var zaehler = <String, int>{};
  for (final w in 'a b a c a b'.split(' ')) {
    zaehler[w] = (zaehler[w] ?? 0) + 1;
  }
  print(zaehler);
  var sortiert = zaehler.entries.toList()..sort((a, b) => b.value.compareTo(a.value));
  print(sortiert.map((e) => '${e.key}:${e.value}').join(' '));

  var s = {3, 1, 2, 3, 1};
  s.add(9);
  print('${s.length} ${s.contains(2)} ${s.union({10})} ${s.intersection({1, 9, 7})} ${s.difference({1})}');
}

17 null 3 true
Mia => 17
Zoe => 31
Ben => 9
[Mia, Zoe, Ben] [17, 31, 9]
{MIA: 18, ZOE: 32, BEN: 10}
{Mia: 17, Zoe: 31}
{a: 3, b: 2, c: 1}
a:3 b:2 c:1
4 true {3, 1, 2, 9, 10} {1, 9} {3, 2, 9}

void main() {
  var person = (name: 'Mia', alter: 17);            // benannter Record
  var punkt = (3, 4);                               // positioneller Record
  print('${person.name} ${person.alter} ${punkt.$1} ${punkt.$2}');
  var (x, y) = punkt;
  var (:name, :alter) = person;
  print('$x $y $name $alter');

  List<int> wert = [1, 2, 3];
  switch (wert) {
    case [var a, var b, var c]:
      print('Liste mit drei Elementen: ${a + b + c}');
    case [var a] when a > 10:
      print('ein großes Element');
    default:
      print('anderes');
  }
  var json = {'name': 'Tom', 'tags': ['a', 'b']};
  if (json case {'name': String n, 'tags': [var erstes, ...]}) {
    print('$n $erstes');
  }
}

Mia 17 3 4
3 4 Mia 17
Liste mit drei Elementen: 6
Tom a