X-Git-Url: https://git.ralfj.de/web.git/blobdiff_plain/a6db9a64b8d02f9d54686e46f177b9ed74614762..ce79f527e9ae2a9b9422367f538118ed87fb2a7d:/ralf/_posts/2018-08-07-stacked-borrows.md diff --git a/ralf/_posts/2018-08-07-stacked-borrows.md b/ralf/_posts/2018-08-07-stacked-borrows.md index bf9f9a6..37cdf50 100644 --- a/ralf/_posts/2018-08-07-stacked-borrows.md +++ b/ralf/_posts/2018-08-07-stacked-borrows.md @@ -147,7 +147,7 @@ Shared references with interior mutability do not really have any restrictions i For every location in memory, we keep track of a stack of borrows (`Uniq(_)` or `Raw`), and potentially "top off" this stack by freezing the location. A frozen location is never written to, and no `Uniq` is pushed. -Whenever a mutable reference is created, a matching `Uniq` is pushed onto the stack for every location "covered by" the reference -- i.e., the locations that would be accessed when the reference is used (starting at where it points to, and going on for `mem::size_of::` many bytes). +Whenever a mutable reference is created, a matching `Uniq` is pushed onto the stack for every location "covered by" the reference -- i.e., the locations that would be accessed when the reference is used (starting at where it points to, and going on for `size_of_val` many bytes). Whenever a shared reference is created, if there is no interior mutability, we freeze the locations if they are not already frozen. If there is interior mutability, we just push a `Raw`. Whenever a raw pointer is created from a mutable reference, we push a `Raw`. @@ -239,7 +239,7 @@ It is also needed to explain why we can put the [`noalias` parameter attribute]( Consider the following code: {% highlight rust %} -fn demo5(x: &mut i32, y: usize) -> i32 { +fn demo5(x: &mut i32, y: usize) { *x = 42; foo(y); } @@ -336,8 +336,11 @@ impl MemoryByte { self.frz_since.map_or(false, |loc_t| loc_t <= acc_t), Mut(acc_m) => // Raw pointers are fine with frozen locations. This is important because &Cell is raw! - (acc_m.is_raw() && self.frozen_since.is_some()) || - self.borrows.last().map_or(false, |loc_itm| loc_itm == Mut(acc_m)), + if self.frozen_since.is_some() { + acc_m.is_raw() + } else { + self.borrows.last().map_or(false, |loc_itm| loc_itm == Mut(acc_m)) + } } }