# Unsafety

Unsafe operations are those that potentially violate the memory-safety guarantees of Rust's static semantics.

The following language level features cannot be used in the safe subset of Rust:

- Dereferencing a raw pointer.
- Reading or writing a mutable static variable.
- Reading a field of a `union`, or writing to a field of a union that isn't `Copy`.
- Calling an unsafe function (including an intrinsic or foreign function).
- Implementing an unsafe trait.