These parts of the language are considered unsafe:
- Code involving raw pointers: the Pointer type and pointerof.
- The allocate class method.
- Code involving C bindings
- Uninitialized variable declaration
"Unsafe" means that memory corruption, segmentation faults and crashes are possible to achieve. For example:
a = 1 ptr = pointerof(a) ptr[100_000] = 2 # undefined behaviour, probably a segmentation fault
However, regular code usually never involves pointer manipulation or uninitialized variables. And C bindings are usually wrapped in safe wrappers that include null pointers and bounds checks.
No language is 100% safe: some parts will inevitably be low-level, interface with the operating system and involve pointer manipulation. But once you abstract that and operate on a higher level, and assume (after mathematical proof or thorough testing) that the lower grounds are safe, you can be confident that your entire codebase is safe.