Add a widget between each pair of widgets in a list of widgets.

helpers.dart

/// Extension on Iterable<Widget> to add a specified widget between each pair of widgets.
extension WidgetIterableExtension on Iterable<Widget> {
  List<Widget> addBetween(Widget child) {
    final iterator = this.iterator;
    final result = <Widget>[];

    if (iterator.moveNext()) result.add(iterator.current);

    while (iterator.moveNext()) {
      result
        ..add(child)
        ..add(iterator.current);
    }

    return result;
  }
}