I hope you now have a clear idea of the basic structure of the model I am proposing: The stack of borrows, the freeze flag, and references tagged with the time at which they got created.
The full model is not quite as simple, but it is not much more complicated either.
-We need two add just two more concepts: Retagging and barriers.
+We need to add just two more concepts: Retagging and barriers.
### 4.1 Retagging
- Compute `new_bor` from `new_tag` and the type of the reference being created.
- `reactivate(bor)`.
- If this is a function argument coming in: `loc.borrows.push(FnBarrier(stack_height))`.
- - `initiate(new_bor)`. Note that this is a NOP if `new_bor` is already active -- in particular, if the location is frozen and this is a shared reference with interior mutability, we do *not* push anything on top of the barrier. This is important, because we do not want to push that might unfreeze the location when being reactivated.
+ - `initiate(new_bor)`. Note that this is a NOP if `new_bor` is already active -- in particular, if the location is frozen and this is a shared reference with interior mutability, we do *not* push anything on top of the barrier. This is important, because any reactivation that unfreezes this location must lead to UB while the barrier is still present.
- Change reference tag to `new_tag`.
* Any time a raw pointer is created from a reference, we might have to do a raw reborrow.
- `reactivate(bor)`.
projects / web.git / blobdiff