Unsafe operations are those that can 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] or [external] static variable.
• Accessing a field of a union, other than to assign to it.
• Calling an unsafe function (including an intrinsic or foreign function).
• Implementing an unsafe trait.