In addition to the original System.Interactive library, and the System.Interactive.Async library that added the same functionality for IAsyncEnumerable<T>, the Ix.NET project also includes System.Linq.Async, which defines for IAsyncEnumerable<T> the same LINQ operators that are built into the .NET runtime libraries for IEnumerable<T>.
Removed various IEnumerable<T> min and max extension methods because .NET 6.0 now has built-in equivalents.
Fixed bug causing duplicate emissions from Delay.
System.Linq.Async adds support for C# 8.0's nullable reference types feature.
Ix Async 4.0 has a breaking change from prior versions due to IAsyncEnumerable<T> being added to the .NET runtime libraries. In earlier versions, Ix Async defined its own version of this interface, but v4.0 has been modified to use the definition now built into the runtime. This enables the IAsyncEnumerable implementations in Ix Async to be consumed by the async streams language feature that was added in C# 8. This means for .NET Standard 2.1 and .NET Core 3 targets, we use the in-box interfaces for IAsyncEnumerable<T> and friends. On other platforms, we use the IAsyncEnumerable definition from Microsoft.Bcl.AsyncInterfaces, supplying a full implementation of the Rx-like LINQ operators Ix has long defined for IEnumerable<T>. The types will unify to the system ones where the platform provides it.
The .NET runtime libraries did not add a full LINQ to Objects implementation for IAsyncEnumerable<T>. Whereas IEnumerable<T> offers standard operators such as Where, Single, and GroupBy, enabling use of the LINQ query expression syntax, this is not available out of the box with .NET for IAsyncEnumerable<T>. Since earlier versions of this library had already done most of the relevant work to implement these operators on its pre-v4.0 version of IAsyncEnumerable<T>, v4.0 of Ix also builds the System.Linq.Async library, making LINQ to Objects available for IAsyncEnumerable<T>.