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.observable;
  
  import io.reactivex.rxjava3.core.*;
  import io.reactivex.rxjava3.exceptions.Exceptions;
  import io.reactivex.rxjava3.plugins.RxJavaPlugins;
  
  import java.util.Objects;
  
  /**
   * Allows lifting operators into a chain of Observables.
   *
   * <p>By having a concrete ObservableSource as lift, operator fusing can now identify
   * both the source and the operation inside it via casting, unlike the lambda version of this.
   *
   * @param <T> the upstream value type
   * @param <R> the downstream parameter type
   */
  public final class ObservableLift<R, T> extends AbstractObservableWithUpstream<T, R> {
      /** The actual operator. */
      final ObservableOperator<? extends R, ? super T> operator;
  
      public ObservableLift(ObservableSource<T> source, ObservableOperator<? extends R, ? super T> operator) {
          super(source);
          this.operator = operator;
      }
  
      @Override
      public void subscribeActual(Observer<? super R> observer) {
          Observer<? super T> liftedObserver;
          try {
              liftedObserver = Objects.requireNonNull(operator.apply(observer), "Operator " + operator + " returned a null Observer");
          } catch (NullPointerException e) { // NOPMD
              throw e;
          } catch (Throwable e) {
              Exceptions.throwIfFatal(e);
              // can't call onError because no way to know if a Disposable has been set or not
              // can't call onSubscribe because the call might have set a Disposable already
              RxJavaPlugins.onError(e);
  
              NullPointerException npe = new NullPointerException("Actually not, but can't throw other exceptions due to RS");
              npe.initCause(e);
              throw npe;
          }
  
          source.subscribe(liftedObserver);
      }
  }
  