Combine two list into one with cross order, example: [A,B,C], [D,E,F] => [A,D,B,E,C,F]

dart-list-merge-extension.dart

import 'dart:math';

extension ListExtension<R> on List<R> {
  // combine two list
  // [A,B,C], [D,E,F] => [A,D,B,E,C,F]
  List<R> merge(List<R> list) {
    List<R> output = [];

    var minLength = min(length, list.length);
    var maxLength = max(length, list.length);

    for (var i = 0; i < minLength; i++) {
      output.add(this[i]);
      output.add(list[i]);
    }

    List<R> longer = length > list.length ? this : list;
    for (var i = minLength; i < maxLength; i++) {
      output.add(longer[i]);
    }
    return output;
  }

  // join the list
  // [A,B,C], D => [A,D,B,C,D]
  List<R> joinList(R item) {
    return merge(List.generate(length, (index) => item));
  }

  Iterable<MapEntry<int, R>> entry() sync* {
    int index = 0;
    for (R item in this) {
      yield MapEntry(index, item);
      index = index + 1;
    }
  }
}