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.
/**
 * 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.internal.operators.observable;

import io.reactivex.*;
import io.reactivex.exceptions.Exceptions;
import io.reactivex.internal.functions.ObjectHelper;
import io.reactivex.plugins.RxJavaPlugins;

Allows lifting operators into a chain of Observables.
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.
Type parameters:
<T> – the upstream value type
<R> – the downstream parameter type/**
 * 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. /** 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 = ObjectHelper.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);
    }
}