Attempt to explain that &mut cannot alias #1198
Conversation
This is a clumsy attempt at making the "`&mut` is an exclusive reference" part of the aliasing rule more discoverable. I feel like this is an inherent property of the type so I was surprised to not find that information here. This is echoing parts of the docs for [UnsafeCell] and [ptr::as_mut], so another place where a newcomer could potentially get this info. I think it's easy for learners to assume that `&mut` can alias since many popular languages have comparatively lax aliasing rules. [UnsafeCell]: https://doc.rust-lang.org/stable/std/cell/struct.UnsafeCell.html [ptr::as_mut]: https://doc.rust-lang.org/std/primitive.pointer.html#method.as_mut-1
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So I just saw rust-lang/unsafe-code-guidelines#133 and realized that the way I'm explaining this is maybe too restrictive. What I wanted to do is to add another place where people can discover the current rules, even though not everything is worked out at the moment. Maybe the reference is not a good place to raise awareness about Stacked Borrows so I'm closing this. I'll point people at other pieces of documentation scattered around that hint that the current aliasing rules. |
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Stacked borrows is implemented in miri, but rustc is more permissive than it. The actual rules aren't really well known (and I think they're inconsistent in the same way that clang's is), but stacked borrows is a set of rules that works on top of it. And then there's Ganka's "quit transmuting integers to pointers" thing on top of that that miri now has a flag to run under as well. |
This is a clumsy attempt at making the "
&mutis an exclusivereference" part of the aliasing rule more discoverable. I feel like this
is an inherent property of the type so I was surprised to not find that
information here. This is echoing parts of the docs for UnsafeCell and
ptr::as_mut, so another place where a newcomer could potentially get
this info.
I think it's easy for learners to assume that
&mutcan alias sincemany popular languages have comparatively lax aliasing rules.
Do you also think adding this here make sense? Maybe I only think so because I've been thinking about this recently.