rust-too-many-lists-book/src/third.rs
2019-03-13 09:33:34 -04:00

110 lines
2.2 KiB
Rust

//! # A Persistent Stack
use std::rc::Rc;
pub struct List<T> {
head: Link<T>,
}
pub struct Iter<'a, T:'a> {
next: Option<&'a Node<T>>,
}
type Link<T> = Option<Rc<Node<T>>>;
struct Node<T> {
elem: T,
next: Link<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,
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
})
}
}
impl<T> Drop for List<T> {
fn drop(&mut self) {
let mut head = self.head.take();
while let Some(node) = head {
if let Ok(mut node) = Rc::try_unwrap(node) {
head = node.next.take();
} else {
break;
}
}
}
}
#[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));
}
}