Collections (List, Map, Set)

Code

// List
var nums = [1, 2, 3, 4, 5];
nums.add(6);
nums.addAll([7, 8]);
var doubled = nums.map((n) => n * 2).toList();
var evens = nums.where((n) => n % 2 == 0).toList();
var sum = nums.reduce((a, b) => a + b);
var firstEven = nums.firstWhere((n) => n % 2 == 0, orElse: () => -1);

// Spread operator
var combined = [...nums, ...[9, 10]];

// Map
var ages = {'Alice': 30, 'Bob': 25};
ages['Carol'] = 28;
ages.forEach((k, v) => print('$k: $v'));
var adults = ages.entries.where((e) => e.value >= 18).map((e) => e.key).toList();

// Set
var unique = <int>{1, 2, 2, 3, 3, 3};  // {1, 2, 3}
unique.add(4);
unique.contains(2);  // true

// Collection if/for (Dart 3)
var showExtra = true;
var items = [
  'item1',
  'item2',
  if (showExtra) 'extra',
  for (var i = 0; i < 3; i++) 'gen$i',
];

Explanation

Dart collections support functional methods (map, where, reduce, fold). map returns a lazy Iterable — call toList() to materialize. Collection if/for (Dart 3) lets you conditionally include elements inline. Spread (...) flattens. firstWhere throws if no match — use orElse. Sets dedupe automatically. Use const collections for compile-time constants.

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