System.Collections work planned for .NET 7

[jeffhandley]

This issue captures the planned work for .NET 7. This list is expected to change throughout the release cycle according to ongoing planning and discussions, with possible additions and subtractions to the scope.

Planned for .NET 7

• Add ImmutableArray Span-based APIs #22928
• Implement ToString() on System.Collections.DictionaryEntry #59292
• Align API surface of immutable collections and their corresponding builder types #822
• [API Proposal]: Add an IAsyncEnumerable<T>.ToEnumerable extension method. #60106

Backlog (roughly in priority order)

• Add a priority queue that supports priority updates #44871
• Eliminate allocations when enumerating empty collections #59596
• Add initial Span<T> access to creation of ImmutableArray<T> #53154
• Add CollectionsMarshal.SetCount API for List<T> #55217
• API proposal: Find methods for ImmutableArray #45366
• System.Collections.Concurrent.Tests timeout failures in CI #37186
• [Mono] Test failed on windows: System.Collections.Concurrent.Tests.BlockingCollectionTests.Test_LargeSize_STA #34360
• [Libraries][Android] Turkish Culture edge case System.Collections.NonGeneric.Tests fail on Android #37069
• Mark StringDictionary as obsolete #889
• Add more Array.Sort test combinations, per #41234 #41376

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Issue Details

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This issue captures the planned work for .NET 7. This list is expected to change throughout the release cycle according to ongoing planning and discussions, with possible additions and subtractions to the scope.

Summary

We are not planning many notable investments into the System.Collections area in .NET 7. We will pursue some performance optimizations, determine if we intend to mark StringDictionary as obsolete, address test issues, refine a few small API proposals, and consider small-to-medium-sized community contributions.

Planned for .NET 7

• Add ImmutableArray Span-based APIs #22928
• Eliminate allocations when enumerating empty collections #59596
• Align API surface of immutable collections and their corresponding builder types #822
• Add initial Span<T> access to creation of ImmutableArray<T> #53154
• Add CollectionsMarshal.SetCount API for List<T> #55217
• Implement ToString() on System.Collections.DictionaryEntry #59292
• API proposal: Find methods for ImmutableArray #45366
• System.Collections.Concurrent.Tests timeout failures in CI #37186
• [Mono] Test failed on windows: System.Collections.Concurrent.Tests.BlockingCollectionTests.Test_LargeSize_STA #34360
• [Libraries][Android] Turkish Culture edge case System.Collections.NonGeneric.Tests fail on Android #37069
• Mark StringDictionary as obsolete #889

Author:	jeffhandley
Assignees:	krwq, jeffhandley, eiriktsarpalis, layomia
Labels:	Epic, area-System.Collections, Priority:3, Team:Libraries
Milestone:	7.0.0

[jeffhandley]

This list in this issue has been edited to reflect changes from our ongoing planning and discussions. The headings have been updated to reflect what is still planned for .NET 7 and what is in the backlog. The list is still expected to change throughout the release cycle with periodic reviews of our plans.

[jeffhandley]

The committed .NET 7 issues are completed. When we wind down .NET 7, we will review the backlog illustrated above (along with other issues in the area) for .NET 8 planning.