A shared_ptr does not prevent iterator invalidation caused by reallocation, because the pointed-to vector is not locked, or in any other form stopped from being

A shared_ptr does not prevent iterator invalidation caused by reallocation, because the pointed-to vector is not locked, or in any other form stopped from being modified. In Rust, when you have an immutable reference to a memory location, you know for certain that it won't be modified by distant code as long as you hold the reference. This guarantee also allows more compiler optimizations, because v[5] has the same value after a function call as before.