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// ==++==
//
// Copyright (c) Microsoft Corporation. All rights reserved.
//
// ==--==
// =+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
//
// SelectQueryOperator.cs
//
// <OWNER>Microsoft</OWNER>
//
// =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
using System.Collections.Generic;
using System.Diagnostics.Contracts;
using System.Threading;
namespace System.Linq.Parallel
{
/// <summary>
/// The operator type for Select statements. This operator transforms elements as it
/// enumerates them through the use of a selector delegate.
/// </summary>
/// <typeparam name="TInput"></typeparam>
/// <typeparam name="TOutput"></typeparam>
internal sealed class SelectQueryOperator<TInput, TOutput> : UnaryQueryOperator<TInput, TOutput>
{
// Selector function. Used to project elements to a transformed view during execution.
private Func<TInput, TOutput> m_selector;
//---------------------------------------------------------------------------------------
// Initializes a new select operator.
//
// Arguments:
// child - the child operator or data source from which to pull data
// selector - a delegate representing the selector function
//
// Assumptions:
// selector must be non null.
//
internal SelectQueryOperator(IEnumerable<TInput> child, Func<TInput, TOutput> selector)
:base(child)
{
Contract.Assert(child != null, "child data source cannot be null");
Contract.Assert(selector != null, "need a selector function");
m_selector = selector;
SetOrdinalIndexState(Child.OrdinalIndexState);
}
internal override void WrapPartitionedStream<TKey>(
PartitionedStream<TInput, TKey> inputStream, IPartitionedStreamRecipient<TOutput> recipient, bool preferStriping, QuerySettings settings)
{
PartitionedStream<TOutput, TKey> outputStream =
new PartitionedStream<TOutput, TKey>(inputStream.PartitionCount, inputStream.KeyComparer, OrdinalIndexState);
for (int i = 0; i < inputStream.PartitionCount; i++)
{
outputStream[i] = new SelectQueryOperatorEnumerator<TKey>(inputStream[i], m_selector);
}
recipient.Receive(outputStream);
}
//---------------------------------------------------------------------------------------
// Just opens the current operator, including opening the child and wrapping it with
// partitions as needed.
//
internal override QueryResults<TOutput> Open(QuerySettings settings, bool preferStriping)
{
QueryResults<TInput> childQueryResults = Child.Open(settings, preferStriping);
return SelectQueryOperatorResults.NewResults(childQueryResults, this, settings, preferStriping);
}
internal override IEnumerable<TOutput> AsSequentialQuery(CancellationToken token)
{
return Child.AsSequentialQuery(token).Select(m_selector);
}
//---------------------------------------------------------------------------------------
// Whether this operator performs a premature merge that would not be performed in
// a similar sequential operation (i.e., in LINQ to Objects).
//
internal override bool LimitsParallelism
{
get { return false; }
}
//---------------------------------------------------------------------------------------
// The enumerator type responsible for projecting elements as it is walked.
//
class SelectQueryOperatorEnumerator<TKey> : QueryOperatorEnumerator<TOutput, TKey>
{
private readonly QueryOperatorEnumerator<TInput, TKey> m_source; // The data source to enumerate.
private readonly Func<TInput, TOutput> m_selector; // The actual select function.
//---------------------------------------------------------------------------------------
// Instantiates a new select enumerator.
//
internal SelectQueryOperatorEnumerator(QueryOperatorEnumerator<TInput, TKey> source, Func<TInput, TOutput> selector)
{
Contract.Assert(source != null);
Contract.Assert(selector != null);
m_source = source;
m_selector = selector;
}
//---------------------------------------------------------------------------------------
// Straightforward IEnumerator<T> methods.
//
internal override bool MoveNext(ref TOutput currentElement, ref TKey currentKey)
{
// So long as the source has a next element, we have an element.
TInput element = default(TInput);
if (m_source.MoveNext(ref element, ref currentKey))
{
Contract.Assert(m_selector != null, "expected a compiled operator");
currentElement = m_selector(element);
return true;
}
return false;
}
protected override void Dispose(bool disposing)
{
m_source.Dispose();
}
}
//-----------------------------------------------------------------------------------
// Query results for a Select operator. The results are indexible if the child
// results were indexible.
//
class SelectQueryOperatorResults : UnaryQueryOperatorResults
{
private Func<TInput, TOutput> m_selector; // Selector function
private int m_childCount; // The number of elements in child results
public static QueryResults<TOutput> NewResults(
QueryResults<TInput> childQueryResults, SelectQueryOperator<TInput, TOutput> op,
QuerySettings settings, bool preferStriping)
{
if (childQueryResults.IsIndexible)
{
return new SelectQueryOperatorResults(childQueryResults, op, settings, preferStriping);
}
else
{
return new UnaryQueryOperatorResults(childQueryResults, op, settings, preferStriping);
}
}
private SelectQueryOperatorResults(
QueryResults<TInput> childQueryResults, SelectQueryOperator<TInput, TOutput> op,
QuerySettings settings, bool preferStriping)
: base(childQueryResults, op, settings, preferStriping)
{
Contract.Assert(op.m_selector != null);
m_selector = op.m_selector;
Contract.Assert(m_childQueryResults.IsIndexible);
m_childCount = m_childQueryResults.ElementsCount;
}
internal override bool IsIndexible
{
get { return true; }
}
internal override int ElementsCount
{
get { return m_childCount; }
}
internal override TOutput GetElement(int index)
{
Contract.Assert(index >= 0);
Contract.Assert(index < ElementsCount);
return m_selector(m_childQueryResults.GetElement(index));
}
}
}
}
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