/*
 * Copyright (c) 2011-2017 Pivotal Software Inc, All Rights Reserved.
 *
 * 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
 *
 *       https://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 reactor.core.publisher;

import java.util.Objects;

import org.reactivestreams.Subscription;
import reactor.core.CoreSubscriber;
import reactor.core.Fuseable;
import reactor.util.annotation.Nullable;

Emits a scalar value if the source sequence turns out to be empty.
Type parameters:
  • <T> – the value type
See Also:
/** * Emits a scalar value if the source sequence turns out to be empty. * * @param <T> the value type * @see <a href="https://github.com/reactor/reactive-streams-commons">Reactive-Streams-Commons</a> */
final class FluxDefaultIfEmpty<T> extends InternalFluxOperator<T, T> { final T value; FluxDefaultIfEmpty(Flux<? extends T> source, T value) { super(source); this.value = Objects.requireNonNull(value, "value"); } @Override public CoreSubscriber<? super T> subscribeOrReturn(CoreSubscriber<? super T> actual) { return new DefaultIfEmptySubscriber<>(actual, value); } @Override public Object scanUnsafe(Attr key) { if (key == Attr.RUN_STYLE) return Attr.RunStyle.SYNC; return super.scanUnsafe(key); } static final class DefaultIfEmptySubscriber<T> extends Operators.MonoSubscriber<T, T> { Subscription s; boolean hasValue; DefaultIfEmptySubscriber(CoreSubscriber<? super T> actual, T value) { super(actual); //noinspection deprecation this.value = value; //we write once, setValue() is NO-OP } @Override @Nullable public Object scanUnsafe(Attr key) { if (key == Attr.PARENT) return s; if (key == Attr.RUN_STYLE) return Attr.RunStyle.SYNC; return super.scanUnsafe(key); } @Override public void request(long n) { super.request(n); s.request(n); } @Override public void cancel() { super.cancel(); s.cancel(); } @Override public void onSubscribe(Subscription s) { if (Operators.validate(this.s, s)) { this.s = s; actual.onSubscribe(this); } } @Override public void onNext(T t) { if (!hasValue) { hasValue = true; } actual.onNext(t); } @Override public void onComplete() { if (hasValue) { actual.onComplete(); } else { complete(this.value); } } @Override public void setValue(T value) { // value is constant. writes from the base class are redundant, and the constant // would always be visible in cancel(), so it will safely be discarded. } @Override public int requestFusion(int requestedMode) { return Fuseable.NONE; // prevent fusion because of the upstream } } }