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Merge pull request #1664 from alecgrieser/cursor-map-continuations
Resolves #1663: Add .map variant to RecordCursor that supports changing a result's continuation
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96 changes: 96 additions & 0 deletions
96
...ecord-layer-core/src/main/java/com/apple/foundationdb/record/cursors/MapResultCursor.java
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,96 @@ | ||
| /* | ||
| * 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. | ||
| */ | ||
|
|
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| package com.apple.foundationdb.record.cursors; | ||
|
|
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| import com.apple.foundationdb.annotation.API; | ||
| import com.apple.foundationdb.record.RecordCursor; | ||
| import com.apple.foundationdb.record.RecordCursorResult; | ||
| import com.apple.foundationdb.record.RecordCursorVisitor; | ||
|
|
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| import javax.annotation.Nonnull; | ||
| import javax.annotation.Nullable; | ||
| import java.util.concurrent.CompletableFuture; | ||
| import java.util.concurrent.Executor; | ||
| import java.util.function.Function; | ||
|
|
||
| /** | ||
| * 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; | ||
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|
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| @Nullable | ||
| private RecordCursorResult<V> nextResult; | ||
|
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| /** | ||
| * 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#map(Function) | ||
| * @see RecordCursor#mapContinuation(Function, ContinuationConvertor, byte[]) | ||
| * @see RecordCursor#mapResult(Function) | ||
| */ | ||
| @API(API.Status.INTERNAL) | ||
| public MapResultCursor(@Nonnull RecordCursor<T> inner, @Nonnull Function<RecordCursorResult<T>, RecordCursorResult<V>> func) { | ||
| this.inner = inner; | ||
| this.func = func; | ||
| } | ||
|
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| @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; | ||
| }); | ||
| } | ||
|
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| @Override | ||
| public void close() { | ||
| inner.close(); | ||
| } | ||
|
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| @Nonnull | ||
| @Override | ||
| public Executor getExecutor() { | ||
| return inner.getExecutor(); | ||
| } | ||
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| @Override | ||
| public boolean accept(@Nonnull final RecordCursorVisitor visitor) { | ||
| if (visitor.visitEnter(this)) { | ||
| inner.accept(visitor); | ||
| } | ||
| return visitor.visitLeave(this); | ||
| } | ||
| } |
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