Return a map iterator which is using a closure in Rust [duplicate]

Answer 1

The trick is not to box the closure, but the iterator as a whole.

fn ceaser_cipher_iter<'a>(data: &'a Vec, key: u8) -> Box + 'a> {
    Box::new(data.iter().map(move |&p| p^key))
}

Note that because the iterator uses a borrow, I had to add lifetime annotations so that the code would pass borrow checking.