System.Linq.AsyncEnumerable in .NET 10

.NET 10 introduces the AsyncEnumerable class, which provides a full set of LINQ extension methods for the IAsyncEnumerable<T> type. This class replaces the community-maintained System.Linq.Async NuGet library, potentially causing compilation errors due to ambiguities.

Version introduced

.NET 10

Previous behavior

Previously, the AsyncEnumerable class in the community-maintained System.Linq.Async package provided LINQ support for IAsyncEnumerable<T>.

New behavior

The AsyncEnumerable class in .NET 10, and in the System.Linq.AsyncEnumerable NuGet package, provides LINQ support for IAsyncEnumerable<T>.

Type of breaking change

This change can affect source compatibility.

Reason for change

IAsyncEnumerable<T> is a commonly used interface, so the platform itself should provide LINQ support for the type. Maintainers of System.Linq.Async and other community members petitioned for inclusion directly in the platform.

Recommended action

If you're upgrading to .NET 10 and your code includes a direct package reference to System.Linq.Async, remove that package reference. For multitargeting both .NET 10 and a previous version, add a package reference to System.Linq.AsyncEnumerable instead.

If System.Linq.Async is consumed indirectly via another package, avoid ambiguity errors by adding <ExcludeAssets> metadata with a value of compile or all:

• To allow transitive use of System.Linq.Async, set <ExcludeAssets> to compile:

  <PackageReference Include="System.Linq.Async" Version="6.0.1">
    <ExcludeAssets>compile</ExcludeAssets>
  </PackageReference>
  

  This configuration prevents direct usage in your code while allowing other packages to continue using System.Linq.Async internally.

• For complete exclusion, set <ExcludeAssets> to all:

  <PackageReference Include="System.Linq.Async" Version="6.0.1">
    <ExcludeAssets>all</ExcludeAssets>
  </PackageReference>
  

  Use this configuration only if you're certain no dependencies require System.Linq.Async at runtime.

Most consuming code should be compatible without changes, but some call sites might need updates to refer to newer names and signatures. For example, a Select call like e.Select(i => i * 2) will work the same before and after. However, the call e.SelectAwait(async (int i, CancellationToken ct) => i * 2) will need to be changed to use Select instead of SelectAwait, as in e.Select(async (int i, CancellationToken ct) => i * 2).

Refer to the System.Linq.AsyncEnumerable API documentation for the full set of LINQ extension methods available for IAsyncEnumerable<T>.

Affected APIs

• System.Linq.AsyncEnumerable
• System.Collections.Generic.IAsyncEnumerable<T>
• System.Linq.Async package (community-maintained)