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.operators.flowable;
  
  import org.reactivestreams.*;
  
  import io.reactivex.rxjava3.annotations.Nullable;
  import io.reactivex.rxjava3.core.*;
  import io.reactivex.rxjava3.internal.subscriptions.SubscriptionHelper;
  import io.reactivex.rxjava3.operators.QueueSubscription;
  
  public final class FlowableIgnoreElements<T> extends AbstractFlowableWithUpstream<T, T> {
  
      public FlowableIgnoreElements(Flowable<T> source) {
          super(source);
      }
  
      @Override
      protected void subscribeActual(final Subscriber<? super T> t) {
          source.subscribe(new IgnoreElementsSubscriber<>(t));
      }
  
      static final class IgnoreElementsSubscriber<T> implements FlowableSubscriber<T>, QueueSubscription<T> {
          final Subscriber<? super T> downstream;
  
          Subscription upstream;
  
          IgnoreElementsSubscriber(Subscriber<? super T> downstream) {
              this.downstream = downstream;
          }
  
          @Override
          public void onSubscribe(Subscription s) {
              if (SubscriptionHelper.validate(this.upstream, s)) {
                  this.upstream = s;
                  downstream.onSubscribe(this);
                  s.request(Long.MAX_VALUE);
              }
          }
  
          @Override
          public void onNext(T t) {
              // deliberately ignored
          }
  
          @Override
          public void onError(Throwable t) {
              downstream.onError(t);
          }
  
          @Override
          public void onComplete() {
              downstream.onComplete();
          }
  
          @Override
          public boolean offer(T e) {
              throw new UnsupportedOperationException("Should not be called!");
          }
  
          @Override
          public boolean offer(T v1, T v2) {
              throw new UnsupportedOperationException("Should not be called!");
          }
  
          @Nullable
          @Override
          public T poll() {
              return null; // empty, always
          }
  
          @Override
          public boolean isEmpty() {
              return true;
          }
  
          @Override
          public void clear() {
              // always empty
          }
  
          @Override
          public void request(long n) {
              // never emits a value
          }
  
          @Override
          public void cancel() {
              upstream.cancel();
          }
  
          @Override
          public int requestFusion(int mode) {
              return mode & ASYNC;
          }
      }
  }
  