021 透過連結串列學Rust之實現迭代器

影片地址：www.bilibili.com/video/av78062009/
相關原始碼：github.com/anonymousGiga/Rust-link...

本節我們來為我們的雙連結串列實現迭代器。

實現程式碼如下：

//實現IntoIter
pub struct IntoIter<T>(List<T>);

impl<T> List<T> {
    pub fn into_iter(self) -> IntoIter<T> {
        IntoIter(self)
    }
}

impl<T> Iterator for IntoIter<T> {
    type Item = T;
    fn next(&mut self) -> Option<Self::Item> {
        self.0.pop_front()
    }
}

impl<T> DoubleEndedIterator for IntoIter<T> {
    fn next_back(&mut self) -> Option<T> {
        self.0.pop_back()
    }
}

    #[test]
    fn into_iter() {
        let mut list = List::new();
        list.push_front(1); 
        list.push_front(2); 
        list.push_front(3);

        let mut iter = list.into_iter();
        assert_eq!(iter.next(), Some(3));
        assert_eq!(iter.next_back(), Some(1));
        assert_eq!(iter.next(), Some(2));
        assert_eq!(iter.next_back(), None);
        assert_eq!(iter.next(), None);
    }

use std::rc::Rc;
use std::cell::{Ref, RefMut, RefCell};

pub struct List<T> {
    head: Link<T>,
    tail: Link<T>,
}

type Link<T> = Option<Rc<RefCell<Node<T>>>>;

struct Node<T> {
    elem: T,
    next: Link<T>,
    prev: Link<T>,
}

impl<T> Node<T> {
    fn new(elem: T) -> Rc<RefCell<Self>> {
        Rc::new(RefCell::new(Node {
            elem: elem,
            prev: None,
            next: None,
        }))
    }
}

impl<T> List<T> {
    pub fn new() -> Self {
        List { head: None, tail: None }
    }

    pub fn push_front(&mut self, elem: T) {
        let node = Node::new(elem);
        match self.head.take() {
            Some(head) => {
                //取可變引用使用borrow_mut
                head.borrow_mut().prev = Some(node.clone());
                node.borrow_mut().next = Some(head);
                self.head = Some(node);
            }
            None => {
                self.tail = Some(node.clone());
                self.head = Some(node);
            }
        }
    }

    pub fn push_back(&mut self, elem: T) {
        let node = Node::new(elem);
        match self.tail.take() {
            Some(tail) => {
                //取可變引用使用borrow_mut
                tail.borrow_mut().next = Some(node.clone());
                node.borrow_mut().prev = Some(tail);
                self.tail = Some(node);
            }
            None => {
                self.head = Some(node.clone());
                self.tail = Some(node);
            }
        }
    }


    pub fn pop_front(&mut self) -> Option<T> {
        self.head.take().map(|node| {
            match node.borrow_mut().next.take() {
                Some(next) => {
                    next.borrow_mut().prev.take();
                    self.head = Some(next);
                }
                None => {
                    self.tail.take();
                }
            }
            //取值使用into_inner
            Rc::try_unwrap(node).ok().unwrap().into_inner().elem
        })
    }

    pub fn pop_back(&mut self) -> Option<T> {
        self.tail.take().map(|node| {
            match node.borrow_mut().prev.take() {
                Some(prev) => {
                    prev.borrow_mut().next.take();
                    self.tail = Some(prev);
                }
                None => {
                    self.head.take();
                }
            }
            //取值使用into_inner
            Rc::try_unwrap(node).ok().unwrap().into_inner().elem
        })
    }

    //pub fn peek_front(&self) -> Option<&T> {
    pub fn peek_front(&self) -> Option<Ref<T>> {
        self.head.as_ref().map(|node| {
            //node.borrow()
            Ref::map(node.borrow(), |node| &node.elem)
        })
    }

    pub fn peek_back(&self) -> Option<Ref<T>> {
        self.tail.as_ref().map(|node| {
            Ref::map(node.borrow(), |node| &node.elem)
        })
    }

    pub fn peek_front_mut(&mut self) -> Option<RefMut<T>> {
        self.head.as_ref().map(|node| {
            RefMut::map(node.borrow_mut(), |node| &mut node.elem)
        })
    }

    pub fn peek_back_mut(&mut self) -> Option<RefMut<T>> {
        self.tail.as_ref().map(|node| {
            RefMut::map(node.borrow_mut(), |node| &mut node.elem)
        })
    }
}

//實現IntoIter
pub struct IntoIter<T>(List<T>);

impl<T> List<T> {
    pub fn into_iter(self) -> IntoIter<T> {
        IntoIter(self)
    }
}

impl<T> Iterator for IntoIter<T> {
    type Item = T;
    fn next(&mut self) -> Option<Self::Item> {
        self.0.pop_front()
    }
}

impl<T> DoubleEndedIterator for IntoIter<T> {
    fn next_back(&mut self) -> Option<T> {
        self.0.pop_back()
    }
}

#[cfg(test)]
mod tests {
    use super::List;

    #[test]
    fn basics() {
        let mut list = List::new();

        assert_eq!(list.pop_front(), None);

        list.push_front(1);
        list.push_front(2);
        list.push_front(3);

        assert_eq!(list.pop_front(), Some(3));
        assert_eq!(list.pop_front(), Some(2));

        list.push_front(4);
        list.push_front(5);

        assert_eq!(list.pop_front(), Some(5));
        assert_eq!(list.pop_front(), Some(4));

        assert_eq!(list.pop_front(), Some(1));
        assert_eq!(list.pop_front(), None);

        // ---- back -----
        assert_eq!(list.pop_back(), None);

        list.push_back(1);
        list.push_back(2);
        list.push_back(3);

        assert_eq!(list.pop_back(), Some(3));
        assert_eq!(list.pop_back(), Some(2));

        list.push_back(4);
        list.push_back(5);

        assert_eq!(list.pop_back(), Some(5));
        assert_eq!(list.pop_back(), Some(4));

        assert_eq!(list.pop_back(), Some(1));
        assert_eq!(list.pop_back(), None);
    }

    #[test]
    fn peek() {
        let mut list = List::new();
        assert!(list.peek_front().is_none());
        assert!(list.peek_back().is_none());
        assert!(list.peek_front_mut().is_none());
        assert!(list.peek_back_mut().is_none());

        list.push_front(1); list.push_front(2); list.push_front(3);

        assert_eq!(&*list.peek_front().unwrap(), &3);
        assert_eq!(&mut *list.peek_front_mut().unwrap(), &mut 3);
        assert_eq!(&*list.peek_back().unwrap(), &1);
        assert_eq!(&mut *list.peek_back_mut().unwrap(), &mut 1);
    }

    #[test]
    fn into_iter() {
        let mut list = List::new();
        list.push_front(1); 
        list.push_front(2); 
        list.push_front(3);

        let mut iter = list.into_iter();
        assert_eq!(iter.next(), Some(3));
        assert_eq!(iter.next_back(), Some(1));
        assert_eq!(iter.next(), Some(2));
        assert_eq!(iter.next_back(), None);
        assert_eq!(iter.next(), None);
    }
}

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