Discussion Thread: DIP 1035-- at system Variables--Final Review

[Paul Backus]

On Monday, 21 February 2022 at 20:30:07 UTC, Dennis wrote:
> On Monday, 21 February 2022 at 19:49:58 UTC, Paul Backus wrote:
>> If there is no benefit to memory-safety from applying `scope`
>> checking to data without indirections, then there is no
>> justification for enabling such checks in all `@safe` code, 
>> even if they may occasionally be "desirable" for other, 
>> non-memory-safety-related reasons.
>
> It is memory-safety related, it allows you to create custom 
> pointer types. A pointer is just an integer under the hood, the 
> idea of indirections and lifetimes is just a compile time idea 
> around a `size_t` which indexes into memory. Why can't we do 
> the same with a `ushort` which indexes into an array?

If the goal is being able to define custom pointer types, then 
the DIP should use that as an example instead of talking about 
file descriptors, and it should explain *exactly* which part of 
the example depends on this feature for memory safety (as the 
other examples do).

I still don't think it's a compelling use-case, though. 
[`TailUnqual`][1] does something very similar, using the `union` 
workaround, and it would not benefit from having access to 
`scope`-checked integers because (a) it stores a `size_t`, so 
eliminating the `union` wouldn't save any space; and (b) it needs 
the `union` for correct GC scanning regardless.

[1]: 
https://gist.github.com/pbackus/1638523a5b6ea3ce2c0a73358cff4dc6