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.Publisher;
  
  import io.reactivex.rxjava3.core.Flowable;
  import io.reactivex.rxjava3.internal.fuseable.HasUpstreamPublisher;
  
  import java.util.Objects;
  
  /**
   * Abstract base class for operators that take an upstream
   * source {@link Publisher}.
   *
   * @param <T> the upstream value type
   * @param <R> the output value type
   */
  abstract class AbstractFlowableWithUpstream<T, R> extends Flowable<R> implements HasUpstreamPublisher<T> {
  
      /**
       * The upstream source Publisher.
       */
      protected final Flowable<T> source;
  
      /**
       * Constructs a FlowableSource wrapping the given non-null (verified)
       * source Publisher.
       * @param source the source (upstream) Publisher instance, not null (verified)
       */
      AbstractFlowableWithUpstream(Flowable<T> source) {
          this.source = Objects.requireNonNull(source, "source is null");
      }
  
      @Override
      public final Publisher<T> source() {
          return source;
      }
  }
  