// add a single item
public ImmutableWidgetList Add(Widget widget)
{
List <Widget> newList = new List <Widget>(_widgets);
ImmutableWidgetList result = new ImmutableWidgetList();
result._widgets = newList;
return(result);
}
// add a range of items.
public ImmutableWidgetList AddRange(IEnumerable <Widget> widgets)
{
List <Widget> newList = new List <Widget>(_widgets);
newList.AddRange(widgets);
ImmutableWidgetList result = new ImmutableWidgetList();
result._widgets = newList;
return(result);
}