rust iter 2

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use std::ptr; use std::fmt::{ Display, Formatter, Result };   pub struct Node {     value: i32,     next: *mut Node }   impl Node {     pub fn new(val: i32) -> Self {         Node {             value: val,             next: ptr::null_mut(),         }     } }   pub struct List {     head: *mut Node }   impl List {     pub fn new() -> Self {        List {            head: ptr::null_mut()        }     }       pub fn add(&mut self, value: i32) {         if self.head == ptr::null_mut() {             self.head = &mut Node::new(value);             return ()         }           let mut _ptr1 = self.head;         // let mut _ptr3 = ptr::null_mut();         // self.head = _ptr3;           unsafe {             while (*_ptr1).next != ptr::null_mut() {                 _ptr1 = (*_ptr1).next;             }         }           let mut _ptr2 = ptr::null_mut();         _ptr2 = &mut Node::new(value);           unsafe {             if (*_ptr1).next == ptr::null_mut() {                 (*_ptr1).next = _ptr2;             }         }     } }   impl Display for List {     fn fmt(&self, f: &mut Formatter) -> Result {         write!(f, "List: {}", self)     } }     impl IntoIterator for List {     type Item = i32;     type IntoIter = ListIntoIterator;       fn into_iter(self) -> Self::IntoIter {         ListIntoIterator { list: self }     } }   pub struct ListIntoIterator {     list: List, }   impl Iterator for ListIntoIterator {     type Item = i32;     fn next(&mut self) -> Option<i32> {         let mut start = self.list.head;         unsafe {             if (*start).next != ptr::null_mut() {                 start = (*start).next;             }                       return Some((*start).value);         }     } }   fn main() {     let mut list1 = List::new();     list1.add(3);     list1.add(6);           // let mut list2 = List::new();       for _i in list1.into_iter() {         println!("{:?}", &_i);         // for j in _i.into_iter() {         //     println!("{}", j);         // }     }; }