operator * method
The existing List + operator only works for lists, so *= is the best we can do
Implementation
List<T> operator *(item) {
if (item is List<T>) {
this.addAll(item);
} else if (item is T) {
this.add(item);
} else if (item == null) {
/// we don't add nulls, may regret this some day
return this;
} else {
throw "Invalid input - must be null, $T, List<$T>";
}
return this;
}