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EmptyResult.java
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EmptyResult.java
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/*
* Copyright (c) 2019 Contributors to the Eclipse Foundation
*
* See the NOTICE file(s) distributed with this work for additional
* information regarding copyright ownership.
*
* This program and the accompanying materials are made available under the
* terms of the Eclipse Public License 2.0 which is available at
* http://www.eclipse.org/legal/epl-2.0
*
* SPDX-License-Identifier: EPL-2.0
*/
package org.eclipse.ditto.internal.utils.persistentactors.results;
import java.util.concurrent.CompletionStage;
import java.util.function.Function;
import org.eclipse.ditto.base.model.signals.events.Event;
/**
* Result without content.
*
* @param <E> type of events.
*/
public final class EmptyResult<E extends Event<?>> implements Result<E> {
private static final Object INSTANCE = new EmptyResult<>();
/**
* Returns the singleton instance of an empty {@link Result}.
*
* @param <E> the type of the event contained in the result.
* @return the empty result instance.
*/
@SuppressWarnings("unchecked")
public static <E extends Event<?>> EmptyResult<E> getInstance() {
return (EmptyResult<E>) INSTANCE;
}
@Override
public void accept(final ResultVisitor<E> visitor) {
visitor.onEmpty();
}
@Override
public <F extends Event<?>> Result<F> map(final Function<E, F> mappingFunction) {
return getInstance();
}
@Override
public <F extends Event<?>> Result<F> mapStages(final Function<CompletionStage<E>, CompletionStage<F>> mappingFunction) {
return getInstance();
}
@Override
public String toString() {
return this.getClass().getSimpleName() + " []";
}
}