For now, this reference is a best-effort document. We strive for validity and completeness, but are not yet there. In the future, the docs and lang teams will work together to figure out how best to do this. Until then, this is a best-effort attempt. If you find something wrong or missing, file an issue or send in a pull request.


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.