code: /*
   * Copyright (c) 2016-present, RxJava Contributors.
   *
   * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in
   * compliance with the License. You may obtain a copy of the License at
   *
   * http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software distributed under the License is
   * distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See
   * the License for the specific language governing permissions and limitations under the License.
   */
  
  package io.reactivex.rxjava3.internal.disposables;
  
  import io.reactivex.rxjava3.annotations.Nullable;
  import io.reactivex.rxjava3.core.*;
  import io.reactivex.rxjava3.operators.QueueDisposable;
  
  /**
   * Represents a stateless empty Disposable that reports being always
   * empty and disposed.
   * <p>It is also async-fuseable but empty all the time.
   * <p>Since EmptyDisposable implements QueueDisposable and is empty,
   * don't use it in tests and then signal onNext with it;
   * use Disposables.empty() instead.
   */
  public enum EmptyDisposable implements QueueDisposable<Object> {
      /**
       * Since EmptyDisposable implements QueueDisposable and is empty,
       * don't use it in tests and then signal onNext with it;
       * use Disposables.empty() instead.
       */
      INSTANCE,
      /**
       * An empty disposable that returns false for isDisposed.
       */
      NEVER
      ;
  
      @Override
      public void dispose() {
          // no-op
      }
  
      @Override
      public boolean isDisposed() {
          return this == INSTANCE;
      }
  
      public static void complete(Observer<?> observer) {
          observer.onSubscribe(INSTANCE);
          observer.onComplete();
      }
  
      public static void complete(MaybeObserver<?> observer) {
          observer.onSubscribe(INSTANCE);
          observer.onComplete();
      }
  
      public static void error(Throwable e, Observer<?> observer) {
          observer.onSubscribe(INSTANCE);
          observer.onError(e);
      }
  
      public static void complete(CompletableObserver observer) {
          observer.onSubscribe(INSTANCE);
          observer.onComplete();
      }
  
      public static void error(Throwable e, CompletableObserver observer) {
          observer.onSubscribe(INSTANCE);
          observer.onError(e);
      }
  
      public static void error(Throwable e, SingleObserver<?> observer) {
          observer.onSubscribe(INSTANCE);
          observer.onError(e);
      }
  
      public static void error(Throwable e, MaybeObserver<?> observer) {
          observer.onSubscribe(INSTANCE);
          observer.onError(e);
      }
  
      @Override
      public boolean offer(Object value) {
          throw new UnsupportedOperationException("Should not be called!");
      }
  
      @Override
      public boolean offer(Object v1, Object v2) {
          throw new UnsupportedOperationException("Should not be called!");
      }
  
      @Nullable
      @Override
      public Object poll() {
          return null; // always empty
      }
  
      @Override
      public boolean isEmpty() {
          return true; // always empty
      }
  
      @Override
      public void clear() {
          // nothing to do
      }
  
      @Override
      public int requestFusion(int mode) {
          return mode & ASYNC;
      }
  
  }
  