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

[Paul Backus]

On Monday, 21 February 2022 at 22:56:30 UTC, Dennis wrote:
> - The compiler currently has a notion of a type that 
> `hasPointers`. The extra complexity of adding a notion 
> `hasSystemVariables` was daunting, but then I thought we could 
> just make them the same. I think that would not only simplify 
> the implementation, but also the feature in general. It makes 
> it easy to draw a parallel to a pointer and a `@system size_t`.

The compiler needs at least two notions: `hasPointers` and 
`hasUnsafeValues`. `hasUnsafeValues` is a superset of 
`hasPointers`, and also includes aggregate types with `@system` 
fields and [`bool`][1].

Since I assume you do not intend to expand `scope` checking to 
`bool`, folding everything into a single concept will not be 
possible.

[1]: https://issues.dlang.org/show_bug.cgi?id=20148

> - Some people asked for the feature (see links in the rationale 
> section)

I've read those links. In one of them, the problem was solved 
using existing DIP 1000 features. The other asks for "unique 
references (and borrow) to plain ints". It is not clear to me 
that `scope` checking for integers would solve either of these 
problems. If you believe it would, then it should not be 
difficult for you to write up an example demonstrating how.