The one that affects you as a programmer most is Iterator invalidation. Iter borrows from the vector, you mutate the vector, iter blows up. Simple really. But a lot of code is like this. Borrow from hashmap, insert into hashmap, the slot gets moved around and your pointer is now invalid. That’s just vectors and hashmaps; imagine the possibilities in a much more complex data structure.

There are compiler optimisations you can do if compiler knows about aliasing, but that’s not so much a software authorship problem. There are some curly problems with passing aliased mutable pointers to a function written for non-aliased inputs, like memcpy and I imagine quite a lot of other code.

But common to all of these things is that it’s pretty hard to figure out if the programmer is the one who has to track the aliasing. In hashmap pointer invalidation, your code might work perfectly for years until some input comes along and finally triggers a shift or a reallocation at the exact right time. (I know this — I recently had to write a lot of C and these are the kinds of issues you get even after you implement some of Rust’s std APIs in C.)