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Check for count through IReadOnlyCollection interface #11805

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Check for count through IReadOnlyCollection interface #11805

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4 changes: 4 additions & 0 deletions src/Build/Collections/CopyOnReadEnumerable.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -72,6 +72,10 @@ public IEnumerator<TResult> GetEnumerator()
#endif
list = new List<TResult>(count);
}
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Copilot AI May 7, 2025

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[nitpick] Consider adding a comment here explaining that this branch is used to pre-allocate the List capacity using IReadOnlyCollection's Count for improved performance.

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}
}
// If the backing enumerable is an IReadOnlyCollection, use its Count property
// to pre-allocate the List capacity for improved performance.

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else if (_backingEnumerable is IReadOnlyCollection<TSource> readOnlyCollection)
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How does this interact with the previous #if net directive please?
Might the if (_backingEnumerable.TryGetNonEnumeratedCount(out int count)) condition make this one basically dead?
Even if it doesn't, it means that in some cases we're mixing two paradigms together I think.

{
list = new List<TResult>(readOnlyCollection.Count);
}
else
{
list = new List<TResult>();
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