code: public boolean add(E e) {
          typeCheck(e);
  
          long oldElements = elements;
          elements |= (1L << ((Enum<?>)e).ordinal());
          return elements != oldElements;
      }
docs: Adds the specified element to this set if it is not already present.
  
  @param e element to be added to this set
  @return <tt>true</tt> if the set changed as a result of the call
  
  @throws NullPointerException if <tt>e</tt> is null