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// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
using System.Collections.Generic;
using System.Diagnostics;
namespace System.Linq
{
public static partial class Enumerable
{
private static IEnumerable<TSource> TakeIterator<TSource>(IEnumerable<TSource> source, int count)
{
Debug.Assert(source is not null && !IsEmptyArray(source));
Debug.Assert(count > 0);
return
source is Iterator<TSource> iterator ? (iterator.Take(count) ?? Empty<TSource>()) :
source is IList<TSource> sourceList ? new IListSkipTakeIterator<TSource>(sourceList, 0, count - 1) :
new IEnumerableSkipTakeIterator<TSource>(source, 0, count - 1);
}
private static IEnumerable<TSource> TakeRangeIterator<TSource>(IEnumerable<TSource> source, int startIndex, int endIndex)
{
Debug.Assert(source is not null && !IsEmptyArray(source));
Debug.Assert(startIndex >= 0 && startIndex < endIndex);
return
source is Iterator<TSource> iterator ? TakeIteratorRange(iterator, startIndex, endIndex) :
source is IList<TSource> sourceList ? new IListSkipTakeIterator<TSource>(sourceList, startIndex, endIndex - 1) :
new IEnumerableSkipTakeIterator<TSource>(source, startIndex, endIndex - 1);
static IEnumerable<TSource> TakeIteratorRange(Iterator<TSource> iterator, int startIndex, int endIndex)
{
Iterator<TSource>? source;
if (endIndex != 0 &&
(source = iterator.Take(endIndex)) is not null &&
(startIndex == 0 || (source = source!.Skip(startIndex)) is not null))
{
return source;
}
return [];
}
}
}
}
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