Introducing Nullable Reference Types in C#. Is there hope for D, too?

[Ola Fosheim Grostad]

On Tuesday, 21 November 2017 at 06:03:33 UTC, Meta wrote:
> I'm not clear on whether he means that Java's type system is 
> unsound, or that the type checking algorithm is unsound. From 
> what I can tell, he's asserting the former but describing the 
> latter.

He claims that type systems with existential rules, hierarchical 
relations between types and null can potentially be unsound. His 
complaint is that if Java had been correctly implemented to the 
letter of the spec then this issue could have led to heap 
corruption if exploited by a malicious programmer.

Runtime checks are part of the type system though, so it isn't 
unsound as implemented as generated JVM does runtime type checks 
upon assignment.

AFAIK the complaint assumes that information from generic 
constraints isn't kept on a separate level.

It is a worst case analysis of the spec...