void apply(ListChange<T> change) {
   change.apply(this.l, this.transf);
 }
 /**
  * Apply all changes since the last {@link #clear()}.
  *
  * @param <U> type of list
  * @param l the list to change.
  * @param transf transform items between this and <code>l</code>.
  * @throws IllegalStateException if this instance doesn't {@link #recordChanges() record changes}.
  */
 @Override
 public <U> void apply(List<U> l, ITransformer<T, U> transf) throws IllegalStateException {
   for (final ListChange<T> change : this.getChanges()) {
     change.apply(l, transf);
   }
 }