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macro_rules! make_list {
($ptr: ident; $(#[$listdoc:meta])*) => {
$(#[$listdoc])*
pub struct List<T> {
head: Option<$ptr<Node<T>>>,
}
struct Node<T> {
elem: T,
next: Option<$ptr<Node<T>>>,
}
list_impl!{$ptr}
make_iter!{}
};
}
macro_rules! list_impl {
($ptr: ident) => {
impl<T> List<T> {
/// Creates a new list.
pub fn new() -> Self {
Self { head: None }
}
/// Returns whether the list is empty.
pub fn is_empty(&self) -> bool {
self.head.is_none()
}
/// Returns the length of the list.
pub fn len(&self) -> usize {
self.iter().len()
}
/// Prepends an element to the front of the list, returning the new list.
pub fn prepend(&self, elem: T) -> Self {
Self { head: Some($ptr::new(Node {
elem,
next: self.head.clone()
}))}
}
/// Returns the list with the first node removed.
pub fn tail(&self) -> Self {
Self {
head: self.head.as_ref().and_then(|node| node.next.clone())
}
}
/// Returns a reference to the first element in the list, if it exists.
pub fn head(&self) -> Option<&T> {
self.head.as_ref().map(|node| &node.elem)
}
/// Creates an iterator that yields shared references to each element in the list.
pub fn iter(&self) -> Iter<'_, T> {
Iter { next: self.head.as_deref() }
}
}
impl<T> Clone for List<T> {
fn clone(&self) -> Self {
Self { head: self.head.clone() }
}
}
use core::fmt;
impl<T: fmt::Debug> fmt::Debug for List<T> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
f.debug_list().entries(self).finish()
}
}
impl<T> Default for List<T> {
fn default() -> Self {
Self::new()
}
}
impl<T> FromIterator<T> for List<T> {
fn from_iter<I: IntoIterator<Item=T>>(iter: I) -> Self {
let mut list = List::new();
for elem in iter {
list = list.prepend(elem);
}
list
}
}
impl<'a, T> IntoIterator for &'a List<T> {
type Item = &'a T;
type IntoIter = Iter<'a, T>;
fn into_iter(self) -> Iter<'a, T> {
Iter { next: self.head.as_deref() }
}
}
impl<T> Drop for List<T> {
fn drop(&mut self) {
let mut cur = self.head.take();
while let Some(node) = cur {
if let Some(mut node) = $ptr::into_inner(node) {
cur = node.next.take();
} else {
break;
}
}
}
}
};
}
macro_rules! make_iter {
() => {
/// An iterator that yields shared references to the elements of a list.
pub struct Iter<'a, T> {
next: Option<&'a Node<T>>
}
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_deref();
&node.elem
})
}
fn size_hint(&self) -> (usize, Option<usize>) {
let mut len = 0;
let mut current = self.next;
while let Some(node) = current {
current = node.next.as_deref();
len += 1;
}
(len, Some(len))
}
}
impl<'a, T> ExactSizeIterator for Iter<'a, T> {
fn len(&self) -> usize {
self.size_hint().0
}
}
};
}
macro_rules! tests {
() => {
#[cfg(test)]
mod tests {
use super::List;
#[test]
fn prepend_tail_head() {
let list = List::new().prepend(1).prepend(2);
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);
let list = list.tail();
assert_eq!(list.head(), None);
}
#[test]
fn is_empty() {
let list = List::new();
assert!(list.is_empty());
let list = list.prepend(1);
assert!(!list.is_empty());
let list = list.tail();
assert!(list.is_empty());
}
#[test]
fn len() {
let list = List::new();
assert_eq!(list.len(), 0);
let list = list.prepend(1).prepend(2);
assert_eq!(list.len(), 2);
let list = list.tail();
assert_eq!(list.len(), 1);
}
#[test]
fn iter() {
let list = List::new().prepend(1).prepend(2);
let mut iter = list.iter();
assert_eq!(iter.next(), Some(&2));
assert_eq!(iter.next(), Some(&1));
assert_eq!(iter.next(), None);
}
}
}
}