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

[Timon Gehr]

On 21.11.2017 07:46, Dmitry Olshansky wrote:
> 
> The spec describes unsound language, the hole in type-system are plugged 
> at VM level by run-time checks.
> 
> Also this jawel:
> 
> Cat[] cats = new Cat[3];
> ...
> Animals[] animals = cats; // the same array
> 
> animals[0] = new Dog();
> 
> cats[0].smth(); // ClassCast exception or some such
> 

Actually, the "java.lang.ArrayStoreException" will be thrown already 
when you attempt to add the dog to the cat array. This is by design 
though (and explicitly supported by the JVM). The reason why the 
null-related Java type system hole does not lead to memory corruption is 
that the JVM does not support generics. (It's all translated to explicit 
type casts that are expected to always succeed, but the JVM still checks 
them.)