safe_cell

This crate exports the SafeCell type, a wrapper type that enables safe exterior mutability for arbitrary contents.

The use case is similar to that of the standard library's UnsafeCell¹ type but, by virtue of being specialized for situations where it can be statically proven that no unsound access occurs, SafeCell is fully usable in safe code. In addition, the implementation is easily proven to be fully sound, making SafeCell a great alternative to UnsafeCell in safety-critical code.

As the implementation is incredibly lightweight and does not make use of any additional synchronization primitives or dynamic borrow tracking, it has negligible overhead (and hence functions as a true "zero-cost abstraction"²).