Symmetric Junk

Симметричный мусор

Alright let's get all that combinatoric symmetry over with.

Что ж, давайте разберёмся со всей этой комбинаторной симметрией.

All we have to do is some basic text replacement:

Всё, что нам нужно, это выполнить простую замену текста:

tail <-> head
next <-> prev
front -> back

Oh, also we need to add _mut variants for peeking.

О, нам также надо написать варианты _mut для методов peek.

use std::cell::{Ref, RefCell, RefMut};

//..

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:

И значительно расширить наши тесты:

#[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_back(), 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.

Есть ли сценарии, которые мы не протестировали? Возможно. Комбинаторное пространство действительно здесь разрослось.

По крайней мере, наш код не явно ошибочный.

> cargo test

     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

Nice. Copy-pasting is the best kind of programming.

Прекрасно. Копи-паста — лучший способ программирования.