[dthul]

Without knowing much Go I believe it's neither a nor b. The pointer to the single element will always stay valid, no matter whether reallocation happens or not (and having a pointer doesn't influence whether reallocation happens or not). Re-allocation might be a confusing word here because afaik it's actually always a new allocation (the old one is not touched) and only if there are no more pointers to the old allocation will the next GC cycle deallocate it. So there is never iterator invalidation like in C++ but of course you still need to be careful because you might accidentally share or not share the same underlying data.

[throwaway894345]

This is correct. A pointer like `p := &x[0]` will always point at the original backing array even if an append on the slice causes the slice to allocate a new backing array. This means that you can update `x[0]` on the new slice without changing `*p`.

https://play.golang.org/p/Hl58VW-Yvhn