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.

fn main() { 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) }) } }
```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.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 => {
}
}
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>> {
RefMut::map(node.borrow_mut(), |node| &mut node.elem)
})
}```

And massively flesh out our tests:

fn main() { #[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); } }
```#[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 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.