Add new shared SelectXXXAsArray helpers #11796
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Add helpers that combine Select And Order/OrderBy/OrderDescending/OrderByDescending to avoid a common LINQ anti-pattern: ```C# List<int> list = [1, 2, 3, 4, 5]; var result = list.Select(x => x * 2).OrderDescendingAsArray(); ``` The code above results in extra allocations by the LINQ Select(...) method, even though the expected results in an ImmutableArray<int>. With these helpers in place, the code above can be written more efficiently as: ```C# List<int> list = [1, 2, 3, 4, 5]; var result = list.SelectAndOrderDescendingAsArray(x => x * 2); ```
LINQ provides a Select(...) overload where the selector takes an int representing the item index. This change adds a similar overload for SelectAsArray.
davidwengier
approved these changes
Apr 28, 2025
src/Shared/Microsoft.AspNetCore.Razor.Utilities.Shared/EnumerableExtensions.cs
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src/Shared/Microsoft.AspNetCore.Razor.Utilities.Shared/EnumerableExtensions.cs
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Use TryGetCount(...) to retrieve a capacity up front before creating a PooledArrayBuilder<T>.
The type tests for ImmutableArray<T> and IReadOnlyList<T> aren't needed in SelectAndOrderXXXAsArray helpers, since those tests are already performed by their calls to SelectAsArray.
ryzngard
approved these changes
Apr 29, 2025
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@dotnet/razor-compiler: Please take a look. Much of these changes are additions to shared code. However, there are some changes in shared methods used by the compiler (e.g. |
ToddGrun
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May 1, 2025
src/Shared/Microsoft.AspNetCore.Razor.Utilities.Shared/ReadOnlyListExtensions.cs
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ToddGrun
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May 1, 2025
src/Shared/Microsoft.AspNetCore.Razor.Utilities.Shared/ReadOnlyListExtensions.cs
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chsienki
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May 1, 2025
333fred
approved these changes
May 1, 2025
@ToddGrun pointed out that the IReadOnlyList<T>.SelectAsArray(...) extension methods really didn't need the complexity of pattern matching and a PooledArrayBuilder<T>. Because we have an IReadOnlyList<T>, we already know the length and can construct the final array up front. This commit makes that change and similarly adjusts the IReadOnlyList<T>.ToArray(), ImmutableArray<T>.SelectAsArray(), and IEnumerable<T>.SelectAsArray() extension methods. Comments have been added throughout to explain specific decisions.
ToddGrun
reviewed
May 2, 2025
| result[index++] = selector(item); | ||
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| Debug.Assert(result.Length == count); |
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An IndexOutOfRangeException would already be thrown in that case, since result is created with a length of count.
This was referenced May 6, 2025
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This adds a handful of new SelectXXXAsArray extension methods and overloads. In particular, there are new
SelectAndOrderXXXAsArraymethods that transform elements and order them in a single pass.