Behavior of "not" keyword in the context of object pattern matching

[Crown0815]

I experimented a little with the not keyword in combination with the object pattern { } which was introduced in C#8. I have come across some behavior that seems weird to me and I would like to make sure that this is intentional.

using something like

if (obj is not { } nonNullObj) return)
nonNullObj.ToString(); // throws a null exception because nonNullObj is null. 

this is counter-intuitive to me since I would have expected

obj is not { } nonNullObj

to be equivalent to

!(obj is { } nonNullObj)

which properly initialized nonNullObj to be not null.

On top of that

if (new object is not { } nonNullObj) return)
nonNullObj.ToString();

actually works fine.

Maybe I am misunderstanding something here? I also opened a ticket on StackOverflow for this issue with some unit tests that reproduce the behavior.

[ufcpp]

Seems like already fixed bug dotnet/roslyn#49708

[Crown0815]

@ufcpp Any idea when the fix will be released?

[333fred]

With 16.9. I don't believe I have a public date that I can share for that.