Check for count through IReadOnlyCollection interface #11805
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Pull Request Overview
This pull request optimizes list allocation in GetEnumerator by utilizing the Count property from an IReadOnlyCollection interface.
- Introduces a code branch to pre-allocate list capacity when the backing enumerable implements IReadOnlyCollection.
- Enhances performance by reducing unnecessary list growth.
| @@ -72,6 +72,10 @@ public IEnumerator<TResult> GetEnumerator() | |||
| #endif | |||
| list = new List<TResult>(count); | |||
| } | |||
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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.
Suggested change
| } | |
| } | |
| // If the backing enumerable is an IReadOnlyCollection, use its Count property | |
| // to pre-allocate the List capacity for improved performance. |
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SimaTian
reviewed
May 9, 2025
| @@ -72,6 +72,10 @@ public IEnumerator<TResult> GetEnumerator() | |||
| #endif | |||
| list = new List<TResult>(count); | |||
| } | |||
| 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.
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Fixes #
Context
Changes Made
Testing
Notes