Proper use of 'unsafe' in Rust is to write safe code that the compiler cannot prove is safe. In fact, this is done to implement many parts of Rust's standard l

Proper use of 'unsafe' in Rust is to write safe code that the compiler cannot prove is safe. In fact, this is done to implement many parts of Rust's standard library. See the split_at_mut example in https://doc.rust-lang.org/book/ch19-01-unsafe-rust.html https://doc.rust-lang.org/book/ch19-01-unsafe-rust.html The spec here is to turn one mutable slice into two non-overlapping mutable slices. The operation does not violate memory safety; we wind up with only one mutable reference to any part of the object. But the compiler does not know how to verify that the programmer has done this correctly. Here, 'unsafe' means 'I certify that this is safe, use that as a lemma to do further checking'.