Prototype of Ownership/Borrowing System for D
newshound2 at digitalmars.com
Tue Nov 26 09:34:55 UTC 2019
On 11/23/2019 3:40 PM, Timon Gehr wrote:
> I don't understand why
> this is not a concern for _your_ designs, which freely admit to being
> uncheckable and unsound. You can't say "@safe means memory safe and this is
> checked by the compiler" and at the same time "@live @safe relies on unchecked
> conventions to ensure memory safety across the @live boundary".
All languages that have an "unsafe" annotation rely on unchecked conventions
when the boundary is crossed.
> I don't think this is the case. The GC-allocated raw pointer allows aliasing
> while @live does not allow aliasing. They have incompatible aliasing
> restrictions. It's like having a mutable and an immutable reference to the same
> memory location.
If I may sum this up, it is you wish to not follow O/B rules in @live functions
when you've got a GC pointer. I suspect it is possible to segregate such
operations into separate, non- at live functions, and I concede that you'll find
In your scheme, this issue is resolved by distinguishing the two by annotating
the non-GC pointers with `scope`.
> What about the fact that it is _optional_ for a /caller/ to respect the smart
> pointer's desired ownership restrictions? That's very restrictive for the smart
> pointer! It won't be able to provide @safe borrowing functionality.
I understand that the salient difference between your scheme and mine is you
attach it to the pointer type while mine attaches it to the function. Pretty
much all of this discussion is about consequences of this difference, so I don't
think it is necessary to go through it point-by-point agreeing with you on those
But yours has problems, too, so the question is which method is better?
1. Doesn't seem to be a way to prevent un-scope pointers from existing and being
2. The splitting pointers down the middle into two categories: scope and
un-scope. This is a very intrusive and drastic change. The only saving grace of
the existing `scope` and `return` annotations is the compiler can infer the vast
bulk of them. Will people accept manually adding `scope` to a big chunk of their
types? I don't know.
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