Enhancements can enable memory-safe reference counting

[tsbockman]

On Thursday, 27 May 2021 at 22:34:53 UTC, IGotD- wrote:
> On Thursday, 27 May 2021 at 22:13:30 UTC, tsbockman wrote:
>>
>> As Paul Backus said earlier, dereferencing a `null` pointer is 
>> formally considered to be memory-safe in D. This is because it 
>> will (with some rare exceptions) crash the program 
>> immediately, rather than corrupting memory and continuing 
>> execution with undefined behavior.
>
> That's "memory-safe" in any language in that case because 
> that's a function of the operating system rather than the 
> language. However, there are exception like if you are 
> dereferencing a null pointer + offset and the offset is large, 
> then you can corrupt memory. This is more rare though.

True. I'm neither defending nor criticizing D's definition of 
"memory safe" here.

My goal is to achieve a similar level of safety and convenience 
with RC and borrowing to what D currently considers `@safe` with 
GC. `@safe` doesn't try to prevent `null` dereferences in GC 
code, so it shouldn't be a requirement for RC code, either.