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Reduce allocations in WhereAsArray IA/IA.Builder extension methods #12051

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Merged
merged 1 commit into from
Jul 23, 2025
Merged

Reduce allocations in WhereAsArray IA/IA.Builder extension methods #12051

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65 changes: 65 additions & 0 deletions src/Shared/Microsoft.AspNetCore.Razor.Utilities.Shared.Test/ImmutableArrayExtensionsTests.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -4,6 +4,7 @@
using System;
using System.Collections.Generic;
using System.Collections.Immutable;
using System.Runtime.InteropServices;
using Xunit;

namespace Microsoft.AspNetCore.Razor.Utilities.Shared.Test;
Expand Down Expand Up @@ -232,4 +233,68 @@ public void InsertRange_WithReferenceTypes_InsertsCorrectly()
Assert.Equal(4, builder.Count);
Assert.Equal(["apple", "cherry", "date", "banana"], builder.ToArray());
}

[Fact]
public void WhereAsArray_ImmutableArray()
{
ImmutableArray<int> data = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
ImmutableArray<int> expected = [2, 4, 6, 8, 10];

var actual = data.WhereAsArray(static x => x % 2 == 0);
Assert.Equal<int>(expected, actual);
}

[Fact]
public void WhereAsArray_ImmutableArray_None()
{
ImmutableArray<int> data = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
ImmutableArray<int> expected = [];

var actual = data.WhereAsArray(static x => false);
Assert.Equal<int>(expected, actual);
}

[Fact]
public void WhereAsArray_ImmutableArray_All()
{
ImmutableArray<int> data = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
var expected = data;

var actual = data.WhereAsArray(static x => true);
Assert.Equal<int>(expected, actual);
Assert.Same(ImmutableCollectionsMarshal.AsArray(expected), ImmutableCollectionsMarshal.AsArray(actual));
}

[Fact]
public void WhereAsArray_ImmutableArrayBuilder()
{
var data = ImmutableArray.CreateBuilder<int>();
data.AddRange(new[] { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 });
ImmutableArray<int> expected = [2, 4, 6, 8, 10];

var actual = data.WhereAsArray(static x => x % 2 == 0);
Assert.Equal<int>(expected, actual);
}

[Fact]
public void WhereAsArray_ImmutableArrayBuilder_None()
{
var data = ImmutableArray.CreateBuilder<int>();
data.AddRange(new[] { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 });
ImmutableArray<int> expected = [];

var actual = data.WhereAsArray(static x => false);
Assert.Equal<int>(expected, actual);
}

[Fact]
public void WhereAsArray_ImmutableArrayBuilder_All()
{
var data = ImmutableArray.CreateBuilder<int>();
data.AddRange(new[] { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 });
var expected = data;

var actual = data.WhereAsArray(static x => true);
Assert.Equal<int>(expected, actual);
}
}
104 changes: 98 additions & 6 deletions src/Shared/Microsoft.AspNetCore.Razor.Utilities.Shared/ImmutableArrayExtensions.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -146,22 +146,114 @@ public static ImmutableArray<TResult> SelectManyAsArray<TSource, TResult>(this I

public static ImmutableArray<T> WhereAsArray<T>(this ImmutableArray<T> source, Func<T, bool> predicate)
{
if (source is [])
using var builder = new PooledArrayBuilder<T>();
var none = true;
var all = true;

var n = source.Length;
for (var i = 0; i < n; i++)
{
return [];
var a = source[i];

if (predicate(a))
{
none = false;
if (all)
{
continue;
}

Debug.Assert(i > 0);
builder.Add(a);
}
else
{
if (none)
{
all = false;
continue;
}

Debug.Assert(i > 0);
if (all)
{
all = false;
for (var j = 0; j < i; j++)
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@davidwengier davidwengier Jul 23, 2025

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Is there any benefit to setting the builder capacity here, to avoid resizing in this loop?

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@ToddGrun ToddGrun Jul 23, 2025

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Probably not. We are mid loop here so don't really know what an appropriate size would be. Additionally, this pooledbuilder is likely already large enough, so it doesn't seem worth the effort to try and make this any smarter in that regard.

{
builder.Add(source[j]);
}
}
}
}

if (all)
{
return source;
}
else if (none)
{
return ImmutableArray<T>.Empty;
}
else
{
return builder.ToImmutableAndClear();
}
}

public static ImmutableArray<T> WhereAsArray<T>(this ImmutableArray<T>.Builder source, Func<T, bool> predicate)
{
using var builder = new PooledArrayBuilder<T>();
var none = true;
var all = true;

foreach (var item in source)
var n = source.Count;
for (var i = 0; i < n; i++)
{
if (predicate(item))
var a = source[i];

if (predicate(a))
{
none = false;
if (all)
{
continue;
}

Debug.Assert(i > 0);
builder.Add(a);
}
else
{
builder.Add(item);
if (none)
{
all = false;
continue;
}

Debug.Assert(i > 0);
if (all)
{
all = false;
for (var j = 0; j < i; j++)
{
builder.Add(source[j]);
}
}
}
}

return builder.ToImmutableAndClear();
if (all)
{
return source.ToImmutable();
}
else if (none)
{
return ImmutableArray<T>.Empty;
}
else
{
return builder.ToImmutableAndClear();
}
}

/// <summary>
Expand Down