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MapResultCursor.java
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MapResultCursor.java
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/*
* MapResultCursor.java
*
* This source file is part of the FoundationDB open source project
*
* Copyright 2015-2022 Apple Inc. and the FoundationDB project authors
*
* 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 com.apple.foundationdb.record.cursors;
import com.apple.foundationdb.annotation.API;
import com.apple.foundationdb.record.RecordCursor;
import com.apple.foundationdb.record.RecordCursorResult;
import com.apple.foundationdb.record.RecordCursorVisitor;
import javax.annotation.Nonnull;
import javax.annotation.Nullable;
import java.util.concurrent.CompletableFuture;
import java.util.concurrent.Executor;
import java.util.function.Function;
import java.util.function.UnaryOperator;
/**
* A cursor that applies a function to the elements of another cursor.
* @param <T> the type of elements of the source cursor
* @param <V> the type of elements of the cursor after applying the function
*/
@API(API.Status.MAINTAINED)
public class MapResultCursor<T, V> implements RecordCursor<V> {
@Nonnull
private final RecordCursor<T> inner;
@Nonnull
private final Function<RecordCursorResult<T>, RecordCursorResult<V>> func;
@Nullable
private RecordCursorResult<V> nextResult;
/**
* Internal constructor. Adopters of the library should call {@link RecordCursor#mapResult(Function) inner.mapResult()}
* or one of its variants instead.
*
* @param inner the inner cursor to apply the function on
* @param func the function to apply
* @see RecordCursor#mapResult(Function)
* @see RecordCursor#map(Function)
* @see RecordCursor#mapContinuation(UnaryOperator)
*/
@API(API.Status.INTERNAL)
public MapResultCursor(@Nonnull RecordCursor<T> inner, @Nonnull Function<RecordCursorResult<T>, RecordCursorResult<V>> func) {
this.inner = inner;
this.func = func;
}
@Nonnull
@Override
public CompletableFuture<RecordCursorResult<V>> onNext() {
if (nextResult != null && !nextResult.hasNext()) {
return CompletableFuture.completedFuture(nextResult);
}
return inner.onNext().thenApply(func)
.thenApply(result -> {
nextResult = result;
return result;
});
}
@Override
public void close() {
inner.close();
}
@Nonnull
@Override
public Executor getExecutor() {
return inner.getExecutor();
}
@Override
public boolean accept(@Nonnull final RecordCursorVisitor visitor) {
if (visitor.visitEnter(this)) {
inner.accept(visitor);
}
return visitor.visitLeave(this);
}
}