On Thu, May 16, 2024 at 9:04 PM Ariel Miculas <amiculas@xxxxxxxxx> wrote: > > From: Alice Ryhl <aliceryhl@xxxxxxxxxx> > > Previously, the `ForeignOwnable` trait had a method called `borrow_mut` > that was intended to provide mutable access to the inner value. However, > the method accidentally made it possible to change the address of the > object being modified, which usually isn't what we want. (And when we > want that, it can be done by calling `from_foreign` and `into_foreign`, > like how the old `borrow_mut` was implemented.) > > In this patch, we introduce an alternate definition of `borrow_mut` that > solves the previous problem. Conceptually, given a pointer type `P` that > implements `ForeignOwnable`, the `borrow_mut` method gives you the same > kind of access as an `&mut P` would, except that it does not let you > change the pointer `P` itself. > > This is analogous to how the existing `borrow` method provides the same > kind of access to the inner value as an `&P`. > > Note that for types like `Arc`, having an `&mut Arc<T>` only gives you > immutable access to the inner `T`. This is because mutable references > assume exclusive access, but there might be other handles to the same > reference counted value, so the access isn't exclusive. The `Arc` type > implements this by making `borrow_mut` return the same type as `borrow`. > > Signed-off-by: Alice Ryhl <aliceryhl@xxxxxxxxxx> > Reviewed-by: Benno Lossin <benno.lossin@xxxxxxxxx> > Reviewed-by: Martin Rodriguez Reboredo <yakoyoku@xxxxxxxxx> > Reviewed-by: Boqun Feng <boqun.feng@xxxxxxxxx> > Link: https://lore.kernel.org/r/20230710074642.683831-1-aliceryhl@xxxxxxxxxx > Signed-off-by: Ariel Miculas <amiculas@xxxxxxxxx> This particular patch something that I have abandoned because I did not end up having any user for it. If you have a user for it, then I recommend that you resend my patch and ask Miguel to take it. Alice
