How to stop Dart's .forEach()?

Question

List data = [1, 2, 3];
data.forEach((value) {
  if (value == 2) {
    // how to stop?
  }
  print(value);
});

Answer 1

Breaking a List

List example = [ 1, 2, 3 ];

for (int value in example) {
  if (value == 2) {
    break;
  }
}

Breaking a Map

If you're dealing with a Map you can't simply get an iterator from the given map, but you can still use a for by applying it to either the values or the keys. Since you sometimes might need the combination of both keys and values, here's an example:

Map example = { 'A': 1, 'B': 2, 'C': 3 };

for (String key in example.keys) {
  if (example[key] == 2 && key == 'B') {
    break;
  }
}

Note that a Map doesn't necessarily have they keys as [ 'A', 'B', 'C' ] use a LinkedHashMap if you want that. If you just want the values, just do example.values instead of example.keys.

Alternatively if you're only searching for an element, you can simplify everything to:

List example = [ 1, 2, 3 ];
int matched = example.firstMatching((e) => e == 2, orElse: () => null);