Final Code

That's all I really have to say on the immutable stack. We're getting pretty good at implementing lists now!

fn main() { use std::rc::Rc; pub struct List<T> { head: Link<T>, } type Link<T> = Option<Rc<Node<T>>>; struct Node<T> { elem: T, next: Link<T>, } pub struct Iter<'a, T:'a> { next: Option<&'a Node<T>>, } impl<T> List<T> { pub fn new() -> Self { List { head: None } } pub fn append(&self, elem: T) -> List<T> { List { head: Some(Rc::new(Node { elem: elem, next: self.head.clone(), }))} } pub fn tail(&self) -> List<T> { List { head: self.head.as_ref().and_then(|node| node.next.clone()) } } pub fn head(&self) -> Option<&T> { self.head.as_ref().map(|node| &node.elem) } pub fn iter(&self) -> Iter<T> { Iter { next: self.head.as_ref().map(|node| &**node) } } } impl<'a, T> Iterator for Iter<'a, T> { type Item = &'a T; fn next(&mut self) -> Option<Self::Item> { self.next.map(|node| { self.next = node.next.as_ref().map(|node| &**node); &node.elem }) } } #[cfg(test)] mod test { use super::List; #[test] fn basics() { let list = List::new(); assert_eq!(list.head(), None); let list = list.append(1).append(2).append(3); assert_eq!(list.head(), Some(&3)); let list = list.tail(); assert_eq!(list.head(), Some(&2)); let list = list.tail(); assert_eq!(list.head(), Some(&1)); let list = list.tail(); assert_eq!(list.head(), None); // Make sure empty tail works let list = list.tail(); assert_eq!(list.head(), None); } #[test] fn iter() { let list = List::new().append(1).append(2).append(3); let mut iter = list.iter(); assert_eq!(iter.next(), Some(&3)); assert_eq!(iter.next(), Some(&2)); assert_eq!(iter.next(), Some(&1)); } } }
use std::rc::Rc;

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

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

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

pub struct Iter<'a, T:'a> {
    next: Option<&'a Node<T>>,
}




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

    pub fn append(&self, elem: T) -> List<T> {
        List { head: Some(Rc::new(Node {
            elem: elem,
            next: self.head.clone(),
        }))}
    }

    pub fn tail(&self) -> List<T> {
        List { head: self.head.as_ref().and_then(|node| node.next.clone()) }
    }

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

    pub fn iter(&self) -> Iter<T> {
        Iter { next: self.head.as_ref().map(|node| &**node) }
    }
}

impl<'a, T> Iterator for Iter<'a, T> {
    type Item = &'a T;

    fn next(&mut self) -> Option<Self::Item> {
        self.next.map(|node| {
            self.next = node.next.as_ref().map(|node| &**node);
            &node.elem
        })
    }
}



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

    #[test]
    fn basics() {
        let list = List::new();
        assert_eq!(list.head(), None);

        let list = list.append(1).append(2).append(3);
        assert_eq!(list.head(), Some(&3));

        let list = list.tail();
        assert_eq!(list.head(), Some(&2));

        let list = list.tail();
        assert_eq!(list.head(), Some(&1));

        let list = list.tail();
        assert_eq!(list.head(), None);

        // Make sure empty tail works
        let list = list.tail();
        assert_eq!(list.head(), None);

    }

    #[test]
    fn iter() {
        let list = List::new().append(1).append(2).append(3);

        let mut iter = list.iter();
        assert_eq!(iter.next(), Some(&3));
        assert_eq!(iter.next(), Some(&2));
        assert_eq!(iter.next(), Some(&1));
    }
}