fn main() {
    let vec = [1, 2, 3];
    let mut iter = vec.into_iter().peekable();

    while let Some(i) = iter.next() {
        let mut next = -1;

        if let Some(peek) = iter.peek() {
            next = **peek;
            let ptr: *mut i32 = *peek as *const i32 as *mut i32;
            unsafe { *ptr = *peek + 1 }
        }

        println!("value: {}, next: {:?}", i, next);
    }
}