From d30b36efc528e7391357d8d2f599c6cf2e427fd2 Mon Sep 17 00:00:00 2001 From: Ralf Jung Date: Tue, 16 Jul 2019 14:47:51 +0200 Subject: [PATCH] state also in the intro that UnsafeCell has no effect on &mut --- src/libcore/cell.rs | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff --git a/src/libcore/cell.rs b/src/libcore/cell.rs index f74e945b3cc1b..0aaf5269a3d47 100644 --- a/src/libcore/cell.rs +++ b/src/libcore/cell.rs @@ -1412,8 +1412,9 @@ impl fmt::Display for RefMut<'_, T> { /// If you have a reference `&SomeStruct`, then normally in Rust all fields of `SomeStruct` are /// immutable. The compiler makes optimizations based on the knowledge that `&T` is not mutably /// aliased or mutated, and that `&mut T` is unique. `UnsafeCell` is the only core language -/// feature to work around this restriction. All other types that allow internal mutability, such as -/// `Cell` and `RefCell`, use `UnsafeCell` to wrap their internal data. +/// feature to work around the restriction that `&T` may not be mutated. All other types that +/// allow internal mutability, such as `Cell` and `RefCell`, use `UnsafeCell` to wrap their +/// internal data. There is *no* legal way to obtain aliasing `&mut`, not even with `UnsafeCell`. /// /// The `UnsafeCell` API itself is technically very simple: it gives you a raw pointer `*mut T` to /// its contents. It is up to _you_ as the abstraction designer to use that raw pointer correctly.