interface ExecutionListWrapper {
    void add(Runnable runnable, Executor executor);

    void execute();

    /** Returns the underlying implementation, useful for the Footprint benchmark. */
    Object getImpl();
  }

  enum Impl {
    NEW {
      @Override
      ExecutionListWrapper newExecutionList() {
        return new ExecutionListWrapper() {
          final ExecutionList list = new ExecutionList();

    String name();
  }

  public interface InternerImplEnum {
    <E> Interner<E> create(Collection<E> contents);

    String name();
  }

  public enum SetImpl implements CollectionsImplEnum {
    HashSetImpl {
      @Override
      public <E extends Comparable<E>> Set<E> create(Collection<E> contents) {
        return new HashSet<E>(contents);
      }
    },