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.fuseable;
  
  import io.reactivex.rxjava3.annotations.NonNull;
  import io.reactivex.rxjava3.operators.QueueDisposable;
  import io.reactivex.rxjava3.operators.QueueFuseable;
  import io.reactivex.rxjava3.operators.QueueSubscription;
  
  /**
   * Represents an empty, async-only {@link QueueFuseable} instance.
   *
   * @param <T> the output value type
   * @since 3.0.0
   */
  public abstract class AbstractEmptyQueueFuseable<T>
  implements QueueSubscription<T>, QueueDisposable<T> {
  
      @Override
      public final int requestFusion(int mode) {
          return mode & ASYNC;
      }
  
      @Override
      public final boolean offer(@NonNull T value) {
          throw new UnsupportedOperationException("Should not be called!");
      }
  
      @Override
      public final boolean offer(@NonNull T v1, @NonNull T v2) {
          throw new UnsupportedOperationException("Should not be called!");
      }
  
      @Override
      public final T poll() throws Throwable {
          return null; // always empty
      }
  
      @Override
      public final boolean isEmpty() {
          return true; // always empty
      }
  
      @Override
      public final void clear() {
          // always empty
      }
  
      @Override
      public final void request(long n) {
          // no items to request
      }
  
      @Override
      public void cancel() {
          // default No-op
      }
  
      @Override
      public void dispose() {
          // default No-op
      }
  
      @Override
      public boolean isDisposed() {
          return false;
      }
  }
  