[cesarb]

> There's a basic reason for that, namely you can't memcpy a self-referential structure while keeping desired semantics.

You actually can! For instance, consider a struct with two fields: a Vec<T>, and a &T which references one of the elements of the Vec. Moving the struct (which does the memcpy) does not reallocate the Vec, so the reference in the &T would still be valid. But as far as I know there's no way to represent that in safe Rust; the &T in the struct requires a lifetime, and there's no way to represent "the lifetime of the other field" or even "the lifetime of the struct itself" (something like &'self T).

Yeah, you can use an index in my example (replacing the &T by an usize, and looking up on the Vec every time), but it's not a perfect replacement. A reference would always be valid (and always pointing to the same element), while an index can become invalid if the Vec is truncated, or point to a wrong element if an element is inserted or removed before it in the Vec.