009 透過連結串列學習Rust之IntoIter

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

本節我們為連結串列實現迭代器。迭代器Trait的定義如下：

pub trait Iterator {
    type Item;
    fn next(&mut self) -> Option<Self::Item>;
}

對於我們來說，我們要實現以下三個迭代器：

IntoIter - T      //對應元素本身
IterMut - &mut T  //對應元素的可變引用
Iter - &T         //對應元素的引用

下面，我們先實現IntoIter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()
    }
}

加上測試的完整程式碼：

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

type Link<T> = Option<Box<Node<T>>>;

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

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

    pub fn push(&mut self, elem: T) {
        let node = Box::new(Node{
            elem: elem,
            next: self.head.take(),
        });
        self.head = Some(node);
    }

    pub fn pop(&mut self) -> Option<T> {
        self.head.take().map(|node| {
            self.head = node.next;
            node.elem
        })
    }

    pub fn peek(&self) -> Option<&T> {
        //self.head.map(|node| {
        self.head.as_ref().map(|node| {
            &node.elem
        })
    }

    pub fn peek_mut(&mut self) -> Option<&mut T> {
        self.head.as_mut().map(|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()
    }
}

#[cfg(test)]
mod tests {
    use super::List;
    #[test]
    fn basics() {
        let mut list = List::new();
        assert_eq!(list.pop(), None);

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

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

        list.push(4);
        list.push(5);

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

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

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

        assert_eq!(list.peek(), None);
        assert_eq!(list.peek_mut(), None);
        list.push(1); 
        list.push(2); 
        list.push(3);

        assert_eq!(list.peek(), Some(&3));
        assert_eq!(list.peek_mut(), Some(&mut 3));

        //list.peek_mut().map(|&mut value| {
        list.peek_mut().map(|value| { //取指標
            //value = 32
            *value = 32
        });

        assert_eq!(list.peek(), Some(&32));
        assert_eq!(list.pop(), Some(32));
    }

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

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

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