ChunkWhile

main.dart

/*
 * Expando with method extension
 * https://gist.github.com/PlugFox/cd8ba4736c95ada1ab2fe4d3ed220a33
 * https://dartpad.dev/cd8ba4736c95ada1ab2fe4d3ed220a33?id=&null_safety=true
 */

void main() {
  final list = <int>[1, 2, 4, 9, 10, 11, 12, 15, 16, 19, 20, 21];
  print('chunkWhile:');
  list.chunkWhile((a, b) => a + 1 == b).forEach(print);
  print('\n' 'splitWhen:');
  list.splitWhen((a, b) => a + 1 == b).forEach(print);
}

extension ChunkWhileX<T extends Object?> on Iterable<T> {
  Iterable<List<T>> chunkWhile(bool Function(T a, T b) test) sync* {
    final i = iterator;
    var list = i.moveNext() ? <T>[i.current] : <T>[];
    while (i.moveNext()) {
      if (test(list.last, i.current)) {
        list.add(i.current);
      } else {
        yield list;
        list = <T>[i.current];
      }
    }
    if (list.isNotEmpty) yield list;
  }

  Iterable<List<T>> splitWhen(bool Function(T a, T b) test) =>
      chunkWhile((a, b) => !test(a, b));
}