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Avoid CollectionsMarshal.AsSpan for derived List<T> in Linq #118682

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Avoid CollectionsMarshal.AsSpan for derived List<T> in Linq #118682

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2 changes: 1 addition & 1 deletion src/libraries/System.Linq/src/System/Linq/Enumerable.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -55,7 +55,7 @@ internal static bool TryGetSpan<TSource>(this IEnumerable<TSource> source, out R
{
span = Unsafe.As<TSource[]>(source);
}
else if (source.GetType() == typeof(List<TSource>))
else if (source.GetType() == typeof(List<TSource>)) // avoid accidentally bypassing a derived type's reimplementation of IEnumerable<T>
{
span = CollectionsMarshal.AsSpan(Unsafe.As<List<TSource>>(source));
}
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5 changes: 3 additions & 2 deletions src/libraries/System.Linq/src/System/Linq/Select.cs
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Expand Up @@ -4,6 +4,7 @@
using System.Collections.Generic;
using System.Diagnostics;
using System.Diagnostics.CodeAnalysis;
using System.Runtime.CompilerServices;
using static System.Linq.Utilities;

namespace System.Linq
Expand Down Expand Up @@ -52,9 +53,9 @@ public static IEnumerable<TResult> Select<TSource, TResult>(
return new ArraySelectIterator<TSource, TResult>(array, selector);
}

if (source is List<TSource> list)
if (source.GetType() == typeof(List<TSource>)) // avoid accidentally bypassing a derived type's reimplementation of IEnumerable<T>
{
return new ListSelectIterator<TSource, TResult>(list, selector);
return new ListSelectIterator<TSource, TResult>(Unsafe.As<List<TSource>>(source), selector);
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Isn't this something for JIT to fix instead?

cc @EgorBo

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I see no difference locally from this change

}

return new IListSelectIterator<TSource, TResult>(ilist, selector);
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65 changes: 24 additions & 41 deletions src/libraries/System.Linq/src/System/Linq/ToCollection.cs
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Expand Up @@ -148,42 +148,34 @@ public static Dictionary<TKey, TSource> ToDictionary<TSource, TKey>(this IEnumer
ThrowHelper.ThrowArgumentNullException(ExceptionArgument.keySelector);
}

Dictionary<TKey, TSource> dict;

if (source.TryGetNonEnumeratedCount(out int capacity))
{
if (capacity == 0)
{
return new Dictionary<TKey, TSource>(comparer);
}

if (source is TSource[] array)
if (source.TryGetSpan(out ReadOnlySpan<TSource> span))
{
return SpanToDictionary(array, keySelector, comparer);
}
dict = new Dictionary<TKey, TSource>(span.Length, comparer);
foreach (TSource element in span)
{
dict.Add(keySelector(element), element);
}

if (source is List<TSource> list)
{
ReadOnlySpan<TSource> span = CollectionsMarshal.AsSpan(list);
return SpanToDictionary(span, keySelector, comparer);
return dict;
}
}

Dictionary<TKey, TSource> d = new Dictionary<TKey, TSource>(capacity, comparer);
dict = new Dictionary<TKey, TSource>(capacity, comparer);
foreach (TSource element in source)
{
d.Add(keySelector(element), element);
dict.Add(keySelector(element), element);
}

return d;
}

private static Dictionary<TKey, TSource> SpanToDictionary<TSource, TKey>(ReadOnlySpan<TSource> source, Func<TSource, TKey> keySelector, IEqualityComparer<TKey>? comparer) where TKey : notnull
{
Dictionary<TKey, TSource> d = new Dictionary<TKey, TSource>(source.Length, comparer);
foreach (TSource element in source)
{
d.Add(keySelector(element), element);
}
return d;
return dict;
}

public static Dictionary<TKey, TElement> ToDictionary<TSource, TKey, TElement>(this IEnumerable<TSource> source, Func<TSource, TKey> keySelector, Func<TSource, TElement> elementSelector) where TKey : notnull =>
Expand All @@ -206,42 +198,33 @@ public static Dictionary<TKey, TElement> ToDictionary<TSource, TKey, TElement>(t
ThrowHelper.ThrowArgumentNullException(ExceptionArgument.elementSelector);
}

Dictionary<TKey, TElement> dict;

if (source.TryGetNonEnumeratedCount(out int capacity))
{
if (capacity == 0)
{
return new Dictionary<TKey, TElement>(comparer);
}

if (source is TSource[] array)
if (source.TryGetSpan(out ReadOnlySpan<TSource> span))
{
return SpanToDictionary(array, keySelector, elementSelector, comparer);
}

if (source is List<TSource> list)
{
ReadOnlySpan<TSource> span = CollectionsMarshal.AsSpan(list);
return SpanToDictionary(span, keySelector, elementSelector, comparer);
dict = new Dictionary<TKey, TElement>(span.Length, comparer);
foreach (TSource element in span)
{
dict.Add(keySelector(element), elementSelector(element));
}
return dict;
}
}

Dictionary<TKey, TElement> d = new Dictionary<TKey, TElement>(capacity, comparer);
dict = new Dictionary<TKey, TElement>(capacity, comparer);
foreach (TSource element in source)
{
d.Add(keySelector(element), elementSelector(element));
dict.Add(keySelector(element), elementSelector(element));
}

return d;
}

private static Dictionary<TKey, TElement> SpanToDictionary<TSource, TKey, TElement>(ReadOnlySpan<TSource> source, Func<TSource, TKey> keySelector, Func<TSource, TElement> elementSelector, IEqualityComparer<TKey>? comparer) where TKey : notnull
{
Dictionary<TKey, TElement> d = new Dictionary<TKey, TElement>(source.Length, comparer);
foreach (TSource element in source)
{
d.Add(keySelector(element), elementSelector(element));
}
return d;
return dict;
}

public static HashSet<TSource> ToHashSet<TSource>(this IEnumerable<TSource> source) => source.ToHashSet(comparer: null);
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5 changes: 3 additions & 2 deletions src/libraries/System.Linq/src/System/Linq/Where.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -3,6 +3,7 @@

using System.Collections.Generic;
using System.Diagnostics;
using System.Runtime.CompilerServices;
using static System.Linq.Utilities;

namespace System.Linq
Expand Down Expand Up @@ -36,9 +37,9 @@ public static IEnumerable<TSource> Where<TSource>(this IEnumerable<TSource> sour
return new ArrayWhereIterator<TSource>(array, predicate);
}

if (source is List<TSource> list)
if (source.GetType() == typeof(List<TSource>))
{
return new ListWhereIterator<TSource>(list, predicate);
return new ListWhereIterator<TSource>(Unsafe.As<List<TSource>>(source), predicate);
}

return new IEnumerableWhereIterator<TSource>(source, predicate);
Expand Down
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