% Symmetric Junk
Alright let's get all that combinatoric symmtery over with.
All we have to do is some basic text replacement:
tail <-> head
next <-> prev
front -> back
Oh, also we need to add _mut
variants for peeking.
pub fn push_back(&mut self, elem: T) {
let new_tail = Node::new(elem);
match self.tail.take() {
Some(old_tail) => {
old_tail.borrow_mut().next = Some(new_tail.clone());
new_tail.borrow_mut().prev = Some(old_tail);
self.tail = Some(new_tail);
}
None => {
self.head = Some(new_tail.clone());
self.tail = Some(new_tail);
}
}
}
pub fn pop_back(&mut self) -> Option<T> {
self.tail.take().map(|old_tail| {
match old_tail.borrow_mut().prev.take() {
Some(new_tail) => {
new_tail.borrow_mut().next.take();
self.tail = Some(new_tail);
}
None => {
self.head.take();
}
}
Rc::try_unwrap(old_tail).ok().unwrap().into_inner().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_back_mut(&mut self) -> Option<RefMut<T>> {
self.tail.as_ref().map(|node| {
RefMut::map(node.borrow_mut(), |node| &mut 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)
})
}
And massively flesh out our tests:
#[test]
fn basics() {
let mut list = List::new();
// Check empty list behaves right
assert_eq!(list.pop_front(), None);
// Populate list
list.push_front(1);
list.push_front(2);
list.push_front(3);
// Check normal removal
assert_eq!(list.pop_front(), Some(3));
assert_eq!(list.pop_front(), Some(2));
// Push some more just to make sure nothing's corrupted
list.push_front(4);
list.push_front(5);
// Check normal removal
assert_eq!(list.pop_front(), Some(5));
assert_eq!(list.pop_front(), Some(4));
// Check exhaustion
assert_eq!(list.pop_front(), Some(1));
assert_eq!(list.pop_front(), None);
// ---- back -----
// Check empty list behaves right
assert_eq!(list.pop_front(), None);
// Populate list
list.push_back(1);
list.push_back(2);
list.push_back(3);
// Check normal removal
assert_eq!(list.pop_back(), Some(3));
assert_eq!(list.pop_back(), Some(2));
// Push some more just to make sure nothing's corrupted
list.push_back(4);
list.push_back(5);
// Check normal removal
assert_eq!(list.pop_back(), Some(5));
assert_eq!(list.pop_back(), Some(4));
// Check exhaustion
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);
}
Are there some cases we're not testing? Probably. The combinatoric space has really blown up here. Our code is at very least not obviously wrong.
> cargo test
Compiling lists v0.1.0 (file:///Users/ABeingessner/dev/too-many-lists/lists)
Running target/debug/lists-5c71138492ad4b4a
running 10 tests
test first::test::basics ... ok
test fourth::test::basics ... ok
test second::test::basics ... ok
test fourth::test::peek ... ok
test second::test::iter ... ok
test third::test::iter ... ok
test second::test::into_iter ... ok
test second::test::iter_mut ... ok
test second::test::peek ... ok
test third::test::basics ... ok
test result: ok. 10 passed; 0 failed; 0 ignored; 0 measured
Doc-tests lists
running 0 tests
test result: ok. 0 passed; 0 failed; 0 ignored; 0 measured
Nice. Copy-pasting is the best kind of programming.