Curriculum Collections & iteration Iterators exercise 2 · mcq-explain

Iterators

rustc rejects this program with error[E0382]: borrow of moved value:xs``. Pick the explanation that names the real cause.

.into_iter() returns owned values, so n must be written as &n to satisfy the println.

The closure inside the for loop borrows xs for its lifetime, blocking subsequent reads.

xs.len() requires &mut self, but xs was declared without mut.

.into_iter() CONSUMES the vector by value — xs is moved into the iterator and dropped at the end of the loop. The subsequent xs.len() reads a moved-out binding, which the borrow checker forbids.

About this theme

Idiomatic Rust often transforms data with iterators instead of manual indexing. The key ownership distinction is .iter(), .iter_mut(), and .into_iter(). Planned exercises: 1. choose .iter() for reading. 2. recognise .into_iter() moves. 3. choose .map(...).collect(). 4. fill .filter. 5. fill .sum::<i32>(). 6. write a map-collect. 7. write an iterator chain that borrows. 8. translate TS map and filter. 9. fix a chain that consumes a vector too early.