r[interior-mut]
r[interior-mut.intro] Sometimes a type needs to be mutated while having multiple aliases. In Rust this is achieved using a pattern called interior mutability.
r[interior-mut.shared-ref] A type has interior mutability if its internal state can be changed through a shared reference to it.
r[interior-mut.no-constraint] This goes against the usual requirement that the value pointed to by a shared reference is not mutated.
r[interior-mut.unsafe-cell]
[std::cell::UnsafeCell<T>] type is the only allowed way to disable
this requirement. When UnsafeCell<T> is immutably aliased, it is still safe to
mutate, or obtain a mutable reference to, the T it contains.
r[interior-mut.mut-unsafe-cell]
As with all other types, it is undefined behavior to have multiple &mut UnsafeCell<T>
aliases.
r[interior-mut.abstraction]
Other types with interior mutability can be created by using UnsafeCell<T> as
a field. The standard library provides a variety of types that provide safe
interior mutability APIs.
r[interior-mut.ref-cell]
For example, [std::cell::RefCell<T>] uses run-time borrow checks to ensure the usual rules around multiple references.
r[interior-mut.atomic]
The [std::sync::atomic] module contains types that wrap a value that is only
accessed with atomic operations, allowing the value to be shared and mutated
across threads.