C#8 handle ref strucs

[JohanLarsson]

Ref structs can now be disposable without implementing the IDisposable interface, simply by having a Dispose method in them.
https://blogs.msdn.microsoft.com/dotnet/2019/01/24/do-more-with-patterns-in-c-8-0/

[jnm2]

So for C# 8, types are disposable with using if:

• IDisposable is implemented, implicitly or explicitly
• Or, the type is a ref struct and public instance Dispose() exists and returns void

And types are disposable with await using if:

• IAsyncDisposable is implemented, implicitly or explicitly
• Or, public instance DisposeAsync() exists and returns an awaitable type with a void result (not just ValueTask)

References

• https://docs.microsoft.com/en-us/dotnet/csharp/whats-new/csharp-8#disposable-ref-structs

• https://docs.microsoft.com/en-us/dotnet/csharp/language-reference/proposals/csharp-8.0/using#pattern-based-using
  Differences between the proposal and C# 8:

  • All types other than ref structs are excluded. (SharpLab
  • Extension methods for Dispose and DisposeAsync are not considered.

• https://docs.microsoft.com/en-us/dotnet/csharp/language-reference/proposals/csharp-8.0/async-streams#pattern-based-compilation

  • The enumerator may optionally expose a DisposeAsync method that may be invoked with no arguments and that returns something that can be awaited and whose GetResult() returns void.

  With DisposeAsync(), the ref struct restriction does not apply. (SharpLab)