Comment by bombela

Pin is a pure compile time abstraction for a single problem: memory safety of self referential struct.

Pin leverages the type system to expose to the programmer receiving a pointer to a Pin'ned object, that this object has some pointer on itself (a self referencial struct). You better be mindful not to move this object to a different memory location unless you know for sure that it is safe to do so. The Pin abstraction makes it harder to forget; and easier to notice during code review; by forcing you to use the keyword unsafe for any operations on the pinned object that could move it around.

In C, there is no such way to warn the programmer besides documentation. It is up to the programmer to be very careful.