Add the latest language features to ‘System.Threading.Channels’

[NiubilityOptimus]

Even in .NET 9.0, it is still not possible to create var channel = Channel.CreateUnbounded<a ref struct>();. The 13.0 syntax already has where T : allows ref struct.

[dotnet-issue-labeler]

I couldn't figure out the best area label to add to this issue. If you have write-permissions please help me learn by adding exactly one area label.

[dotnet-issue-labeler]

I couldn't figure out the best area label to add to this issue. If you have write-permissions please help me learn by adding exactly one area label.

[NiubilityOptimus]

Dear Sir or Miss. This is an e-mail from Johnnie' QQ Mail.Thank you for your E-mail.I apologize that I am unable to respond to you immediately . I will get back to you as soon as I return.

[KalleOlaviNiemitalo]

This does not look feasible. If T is e.g. Span<int>, then it can point to a stackalloc int[1] in the stack of a thread, and if such a value is written to the channel and later read back from there, then the stack frame may have been freed already. If Channel<T>, ChannelWriter<T>, etc. were ref struct types themselves, then the C# compiler could perhaps detect this ref-safety violation; but they are class types.