[nickitolas]

No, this is specifically not creating a mutable reference. So it's fine except for the fact that writing via assignment like this calls the destructor/drop for the old value, if the type has a Drop implementation. That's why &str is fine but String is not, since it will call Drop on a zeroed String (Which is not guaranteed to work) or on an uninitialized String. Using ptr::write instead explicitly does not Drop the old value that is being overwritten.

Basically, if you have something like

    let v = vec![1,2,3];
    v = vec![4,5,6]; // Here vec![1,2,3] is dropped otherwise we would be leaking

[remram]

Do you have a source/explanation for *role not being a mutable reference? What is this expression's type then?

You mention ptr::write() but it is not used here, and I don't see how you could use it to write to a field?

[gulbanana]

(*role) is not a reference at all, it is a value. its type is Role.

[remram]

lvalue not mutable reference, got it. I'm surprised there are contexts where one is fine but the other is UB, but I understand the rule.