/**
   * Invoked when the HTTP connection has been closed normally.
   *
   * No further calls to this listener will be made.
   */
  open fun onClosed(eventSource: EventSource) {
  }

  /**
   * Invoked when an event source has been closed due to an error reading from or writing to the
   * network. Incoming events may have been lost. No further calls to this listener will be made.
   */
  open fun onFailure(

   * @param actual The type that the formal type variable(s) are mapped to. It can be or contain yet
   *     other type variables, in which case these type variables will be further resolved if
   *     corresponding mappings exist in the current {@code TypeResolver} instance.
   */
  public TypeResolver where(Type formal, Type actual) {
    Map<TypeVariableKey, Type> mappings = new HashMap<>();

   * @param actual The type that the formal type variable(s) are mapped to. It can be or contain yet
   *     other type variables, in which case these type variables will be further resolved if
   *     corresponding mappings exist in the current {@code TypeResolver} instance.
   */
  public TypeResolver where(Type formal, Type actual) {
    Map<TypeVariableKey, Type> mappings = new HashMap<>();

   * fewer than {@code k} have been offered, in the order specified by the factory used to create
   * this {@code TopKSelector}.
   *
   * <p>The returned list is an unmodifiable copy and will not be affected by further changes to
   * this {@code TopKSelector}. This method returns in O(k log k) time.
   */
  public List<T> topK() {
    @SuppressWarnings("nullness") // safe because we pass sort() a range that contains real Ts