[RFC] Throwing an exception with null pointers

[Derek Fawcus]

On Wednesday, 16 April 2025 at 08:49:39 UTC, Richard (Rikki) 
Andrew Cattermole wrote:
>> How is out of bounds access related to null pointers throwing 
>> exceptions?
>
> Out of bounds on a slice uses a read barrier to throw an 
> exception.
>
> A read barrier to prevent dereferencing a null pointer is 
> exactly the same concept.
>
> One is 0 or 1.
>
> Second is 0 or N.

Exactly what are you referring to by "read barrier"?

To me it has a specific technical meaning, related to memory 
access and if/when one access may pass another.  It has nothing 
to do with exceptions, but rather the details of how a CPU 
architecture approaches superscalar memory accesses (reads and/or 
writes), and how they are (or may be) re-ordered.

However I would not classify the bounds check performed as part 
of accessing a slice as a "read barrier", rather it is a manual 
range check.

So by "read barrier" for null's do you simply mean having the 
compile generate a "compare to zero" instruction, followed by a 
"jump if zero" to some error path?

If so, then while it may catch errors (and I have no objection to 
optionally generating such null checks); it is not IMO a means of 
error recovery - simply another means of forcing a crash.