Unsafe blocks

These are some guidelines for using unsafe blocks, but is in no way an exhaustive list of everything to avoid in order to use them safely.

• Any resource management (memory, files, sockets, database connections, etc.) needs to be wrapped in an object with a destructor, or it will leak if the stack unwinds. Exposing a close method and never forgetting to call it isn't enough.
• You should be very aware of stack unwinding. If a failure happens, destructors will be called, so objects can't be left in a state where that could be harmful unless it can be guaranteed to never happen.
• An enum (including C-style ones) must only be set to one of the explicitly included discriminant values.
• The rules surrounding mutability should not be broken. If you mutate an object in a method, you can't hide that without using @mut pointers as wrappers. You can also use *mut, but the pointer is still assumed to fall under the mutability rules (just not what it points to).
• You should not work around the restrictions placed on @, ~ and &, instead use * pointers if you can't fit something into the semantics of the safe pointer types.