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< h1 id = "implementing-cursors" > < a class = "header" href = "#implementing-cursors" > Implementing Cursors< / a > < / h1 >
< p > 好了，我们现在讨论 CursorMut。就像我最初的设计一样， < / p >
< ul >
< li > 指向当前节点的指针< / li >
< li > 指向列表的指针< / li >
< li > 当前索引< / li >
< / ul >
< p > 等等，当我们指向 “幽灵 “时，索引是多少？< / p >
< p > 好吧，游标 (cursors)上的索引返回一个 < code > Option< usize> < / code > ， ， ， ， < / p >
< p > 如果你愿意，也可以实现这些东西，但我打算减少所有重复的垃圾和角落情况，只做一个从 ghost 处开始的 cursor_mut 方法，人们可以使用 move_next/move_prev 来获取他们想要的元素（如果你真的愿意，也可以将其封装为 cursor_front） < / p >
< p > 让我们开始吧：< / p >
< p > 非常简单直接，上面的需求列表每一项都有一个字段！< / p >
< pre class = "playground" > < code class = "language-rust edition2021" > < span class = "boring" > #![allow(unused)]
< / span > < span class = "boring" > fn main() {
< / span > pub struct CursorMut< 'a, T> {
cur: Link< T> ,
list: & 'a mut LinkedList< T> ,
index: Option< usize> ,
}
< span class = "boring" > }< / span > < / code > < / pre >
< p > 现在是< code > cursor_mut< / code > 方法:< / p >
< pre class = "playground" > < code class = "language-rust edition2021" > < span class = "boring" > #![allow(unused)]
< / span > < span class = "boring" > fn main() {
< / span > impl< T> LinkedList< T> {
pub fn cursor_mut(& mut self) -> CursorMut< T> {
CursorMut {
list: self,
cur: None,
index: None,
}
}
}
< span class = "boring" > }< / span > < / code > < / pre >
< p > 既然我们从幽灵节点开始，我们所以开始节点都是 < code > None< / code > ，简单明了！下一个是 < code > move_next< / code > ： < / p >
< pre class = "playground" > < code class = "language-rust edition2021" > < span class = "boring" > #![allow(unused)]
< / span > < span class = "boring" > fn main() {
< / span > impl< 'a, T> CursorMut< 'a, T> {
pub fn index(& self) -> Option< usize> {
self.index
}
pub fn move_next(& mut self) {
if let Some(cur) = self.cur {
unsafe {
// We're on a real element, go to its next (back)
self.cur = (*cur.as_ptr()).back;
if self.cur.is_some() {
*self.index.as_mut().unwrap() += 1;
} else {
// We just walked to the ghost, no more index
self.index = None;
}
}
} else if !self.list.is_empty() {
// We're at the ghost, and there is a real front, so move to it!
self.cur = self.list.front;
self.index = Some(0)
} else {
// We're at the ghost, but that's the only element... do nothing.
}
}
}
< span class = "boring" > }< / span > < / code > < / pre >
< p > 所以这有4种有趣的情况： < / p >
< ul >
< li > 正常情况< / li >
< li > 正常情况，但我们移动到了幽灵节点< / li >
< li > 幽灵节点开始，向列表头部节点移动< / li >
< li > 幽灵节点开始，列表是空的，所以什么都不做< / li >
< / ul >
< p > < code > move_prev< / code > 的逻辑完全相同，但前后颠倒，索引变化也颠倒：< / p >
< pre class = "playground" > < code class = "language-rust edition2021" > < span class = "boring" > #![allow(unused)]
< / span > < span class = "boring" > fn main() {
< / span > pub fn move_prev(& mut self) {
if let Some(cur) = self.cur {
unsafe {
// We're on a real element, go to its previous (front)
self.cur = (*cur.as_ptr()).front;
if self.cur.is_some() {
*self.index.as_mut().unwrap() -= 1;
} else {
// We just walked to the ghost, no more index
self.index = None;
}
}
} else if !self.list.is_empty() {
// We're at the ghost, and there is a real back, so move to it!
self.cur = self.list.back;
self.index = Some(self.list.len - 1)
} else {
// We're at the ghost, but that's the only element... do nothing.
}
}
< span class = "boring" > }< / span > < / code > < / pre >
< p > 接下来，让我们添加一些方法来查看游标周围的元素：< code > current< / code > 、< code > peek_next< / code > 和 < code > peek_prev< / code > 。 < strong > 一个非常重要的注意事项< / strong > ：这些方法必须通过 < code > & mut self< / code > 借用我们的游标，并且结果必须与借用绑定。我们不能让用户获得可变引用的多个副本，也不能让他们在持有该引用的情况下使用我们的 insert/remove/split/splice API！ < / p >
< p > 值得庆幸的是，这是 rust 在使用生命周期省略规则时的默认设置，因此我们将默认做正确的事情！< / p >
< pre class = "playground" > < code class = "language-rust edition2021" > < span class = "boring" > #![allow(unused)]
< / span > < span class = "boring" > fn main() {
< / span > pub fn current(& mut self) -> Option< & mut T> {
unsafe {
self.cur.map(|node| & mut (*node.as_ptr()).elem)
}
}
pub fn peek_next(& mut self) -> Option< & mut T> {
unsafe {
self.cur
.and_then(|node| (*node.as_ptr()).back)
.map(|node| & mut (*node.as_ptr()).elem)
}
}
pub fn peek_prev(& mut self) -> Option< & mut T> {
unsafe {
self.cur
.and_then(|node| (*node.as_ptr()).front)
.map(|node| & mut (*node.as_ptr()).elem)
}
}
< span class = "boring" > }< / span > < / code > < / pre >
< h1 id = "split" > < a class = "header" href = "#split" > < a href = "https://rust-unofficial.github.io/too-many-lists/sixth-cursors-impl.html#split" > Split< / a > < / a > < / h1 >
< p > 首先是 split_before 和 split_after， ， ） ： < / p >
< p > 这个逻辑其实并不复杂，所以我们得一步一步来。< / p >
< p > 我发现 split_before 有四种潜在的情况：< / p >
< ul >
< li > 正常情况< / li >
< li > 正常情况，但 prev 是幽灵节点< / li >
< li > 幽灵节点情况，我们返回整个列表，然后变成空列表< / li >
< li > 幽灵节点情况，但列表是空的，所以什么也不做，返回空列表< / li >
< / ul >
< p > 让我们先从极端情况开始。我认为第三种情况< / p >
< pre class = "playground" > < code class = "language-rust edition2021" > < span class = "boring" > #![allow(unused)]
< / span > < span class = "boring" > fn main() {
< / span > mem::replace(self.list, LinkedList::new())
< span class = "boring" > }< / span > < / code > < / pre >
< p > 对不对？我们是空的了，并返回了整个列表，而我们的字段都应该是 “None”， ， ， ！ < / p >
< p > 现在是普通情况……，我需要画下图。最常见的情况是这样的< / p >
< pre > < code class = "language-text" > list.front -> A < -> B < -> C < -> D < - list.back
^
cur
< / code > < / pre >
< p > 我们想变成这样：< / p >
< pre > < code class = "language-text" > list.front -> C < -> D < - list.back
^
cur
return.front -> A < -> B < - return.back
< / code > < / pre >
< p > 因此，我们需要打破当前数据和前一个数据之间的联系，而且……天哪，需要改变的东西太多了。好吧，我只需要把它分成几个步骤，这样我就能说服自己这是有意义的。虽然有点啰嗦，但我至少能说得通：< / p >
< pre class = "playground" > < code class = "language-rust edition2021" > < span class = "boring" > #![allow(unused)]
< / span > < span class = "boring" > fn main() {
< / span > pub fn split_before(& mut self) -> LinkedList< T> {
if let Some(cur) = self.cur {
// We are pointing at a real element, so the list is non-empty.
unsafe {
// Current state
let old_len = self.list.len;
let old_idx = self.index.unwrap();
let prev = (*cur.as_ptr()).front;
// What self will become
let new_len = old_len - old_idx;
let new_front = self.cur;
let new_idx = Some(0);
// What the output will become
let output_len = old_len - new_len;
let output_front = self.list.front;
let output_back = prev;
// Break the links between cur and prev
if let Some(prev) = prev {
(*cur.as_ptr()).front = None;
(*prev.as_ptr()).back = None;
}
// Produce the result:
self.list.len = new_len;
self.list.front = new_front;
self.index = new_idx;
LinkedList {
front: output_front,
back: output_back,
len: output_len,
_boo: PhantomData,
}
}
} else {
// We're at the ghost, just replace our list with an empty one.
// No other state needs to be changed.
std::mem::replace(self.list, LinkedList::new())
}
}
< span class = "boring" > }< / span > < / code > < / pre >
< p > 你可能注意到，我们没有处理 prev 是幽灵节点的情况。但据我所知，其他一切都只是顺便做了正确的事。等我们写测试的时候就知道了！（复制粘贴完成 split_after） < / p >
< h1 id = "splice" > < a class = "header" href = "#splice" > < a href = "https://rust-unofficial.github.io/too-many-lists/sixth-cursors-impl.html#splice" > Splice< / a > < / a > < / h1 >
< p > 还有一个老大难，那就是 splice_before 和 splice_after， ， ， ， ， ， < / p >
< ul >
< li > 如果他们的列表是空的，我们就什么都不用做。< / li >
< li > 如果我们的列表是空的，那么我们的列表就变成了他们的列表。< / li >
< li > 如果我们指向的是幽灵节点，则追加到后面（更改 list.back） < / li >
< li > 如果我们指向的是第一个元素（ ） ， （ ） < / li >
< li > 一般情况下，我们会进行大量的指针操作< / li >
< / ul >
< p > 一般情况：< / p >
< pre > < code class = "language-text" > input.front -> 1 < -> 2 < - input.back
list.front -> A < -> B < -> C < - list.back
^
cur
< / code > < / pre >
< p > 变成这样：< / p >
< pre > < code class = "language-text" > list.front -> A < -> 1 < -> 2 < -> B < -> C < - list.back
< / code > < / pre >
< p > 好的，让我们来写一下：< / p >
< pre class = "playground" > < code class = "language-rust edition2021" > < span class = "boring" > #![allow(unused)]
< / span > < span class = "boring" > fn main() {
< / span > pub fn splice_before(& mut self, mut input: LinkedList< T> ) {
unsafe {
if input.is_empty() {
// Input is empty, do nothing.
} else if let Some(cur) = self.cur {
if let Some(0) = self.index {
// We're appending to the front, see append to back
(*cur.as_ptr()).front = input.back.take();
(*input.back.unwrap().as_ptr()).back = Some(cur);
self.list.front = input.front.take();
// Index moves forward by input length
*self.index.as_mut().unwrap() += input.len;
self.list.len += input.len;
input.len = 0;
} else {
// General Case, no boundaries, just internal fixups
let prev = (*cur.as_ptr()).front.unwrap();
let in_front = input.front.take().unwrap();
let in_back = input.back.take().unwrap();
(*prev.as_ptr()).back = Some(in_front);
(*in_front.as_ptr()).front = Some(prev);
(*cur.as_ptr()).front = Some(in_back);
(*in_back.as_ptr()).back = Some(cur);
// Index moves forward by input length
*self.index.as_mut().unwrap() += input.len;
self.list.len += input.len;
input.len = 0;
}
} else if let Some(back) = self.list.back {
// We're on the ghost but non-empty, append to the back
// We can either `take` the input's pointers or `mem::forget`
// it. Using take is more responsible in case we do custom
// allocators or something that also needs to be cleaned up!
(*back.as_ptr()).back = input.front.take();
(*input.front.unwrap().as_ptr()).front = Some(back);
self.list.back = input.back.take();
self.list.len += input.len;
// Not necessary but Polite To Do
input.len = 0;
} else {
// We're empty, become the input, remain on the ghost
*self.list = input;
}
}
}
< span class = "boring" > }< / span > < / code > < / pre >
< p > 好吧，这个程序真的很可怕，现在真的感觉到 < code > Option< NonNull> < / code > 的痛苦了。但我们可以做很多清理工作。首先，我们可以把这段代码拖到最后。< / p >
< pre class = "playground" > < code class = "language-rust edition2021" > < span class = "boring" > #![allow(unused)]
< / span > < span class = "boring" > fn main() {
< / span > self.list.len += input.len;
input.len = 0;
< span class = "boring" > }< / span > < / code > < / pre >
< p > 好了，现在在分支 “we’ < code > swap< / code > :< / p >
< blockquote >
< p > Use of moved value: < code > input< / code > < / p >
< / blockquote >
< pre class = "playground" > < code class = "language-rust edition2021" > < span class = "boring" > #![allow(unused)]
< / span > < span class = "boring" > fn main() {
< / span > // We're empty, become the input, remain on the ghost
std::mem::swap(self.list, & mut input);
< span class = "boring" > }< / span > < / code > < / pre >
< p > 在我反向思考下面这种情况时，我发现了这个 < code > unwrap< / code > 有问题(因为 cur 的 front 在前面已经被设置为其它值了)： < / p >
< pre class = "playground" > < code class = "language-rust edition2021" > < span class = "boring" > #![allow(unused)]
< / span > < span class = "boring" > fn main() {
< / span > if let Some(0) = self.index {
} else {
let prev = (*cur.as_ptr()).front.unwrap();
}
< span class = "boring" > }< / span > < / code > < / pre >
< p > 这行也是重复的，可以提升:< / p >
< pre class = "playground" > < code class = "language-rust edition2021" > < span class = "boring" > #![allow(unused)]
< / span > < span class = "boring" > fn main() {
< / span > *self.index.as_mut().unwrap() += input.len;
< span class = "boring" > }< / span > < / code > < / pre >
< p > 好了，把上面的问题修改后得到这些：< / p >
< pre class = "playground" > < code class = "language-rust edition2021" > < span class = "boring" > #![allow(unused)]
< / span > < span class = "boring" > fn main() {
< / span > if input.is_empty() {
// Input is empty, do nothing.
} else if let Some(cur) = self.cur {
// Both lists are non-empty
if let Some(prev) = (*cur.as_ptr()).front {
// General Case, no boundaries, just internal fixups
let in_front = input.front.take().unwrap();
let in_back = input.back.take().unwrap();
(*prev.as_ptr()).back = Some(in_front);
(*in_front.as_ptr()).front = Some(prev);
(*cur.as_ptr()).front = Some(in_back);
(*in_back.as_ptr()).back = Some(cur);
} else {
// We're appending to the front, see append to back below
(*cur.as_ptr()).front = input.back.take();
(*input.back.unwrap().as_ptr()).back = Some(cur);
self.list.front = input.front.take();
}
// Index moves forward by input length
*self.index.as_mut().unwrap() += input.len;
} else if let Some(back) = self.list.back {
// We're on the ghost but non-empty, append to the back
// We can either `take` the input's pointers or `mem::forget`
// it. Using take is more responsible in case we do custom
// allocators or something that also needs to be cleaned up!
(*back.as_ptr()).back = input.front.take();
(*input.front.unwrap().as_ptr()).front = Some(back);
self.list.back = input.back.take();
} else {
// We're empty, become the input, remain on the ghost
std::mem::swap(self.list, & mut input);
}
self.list.len += input.len;
// Not necessary but Polite To Do
input.len = 0;
// Input dropped here
< span class = "boring" > }< / span > < / code > < / pre >
< p > 还是不对， ： < / p >
< pre class = "playground" > < code class = "language-rust edition2021" > < span class = "boring" > #![allow(unused)]
< / span > < span class = "boring" > fn main() {
< / span > (*back.as_ptr()).back = input.front.take();
(*input.front.unwrap().as_ptr()).front = Some(back);
< span class = "boring" > }< / span > < / code > < / pre >
< p > 我们使用 < code > take< / code > 拿走了 input.front 的值，然后在下一行将其 < code > unwrap< / code > ！ ， ！ < / p >
< pre class = "playground" > < code class = "language-rust edition2021" > < span class = "boring" > #![allow(unused)]
< / span > < span class = "boring" > fn main() {
< / span > // We can either `take` the input's pointers or `mem::forget`
// it. Using `take` is more responsible in case we ever do custom
// allocators or something that also needs to be cleaned up!
if input.is_empty() {
// Input is empty, do nothing.
} else if let Some(cur) = self.cur {
// Both lists are non-empty
let in_front = input.front.take().unwrap();
let in_back = input.back.take().unwrap();
if let Some(prev) = (*cur.as_ptr()).front {
// General Case, no boundaries, just internal fixups
(*prev.as_ptr()).back = Some(in_front);
(*in_front.as_ptr()).front = Some(prev);
(*cur.as_ptr()).front = Some(in_back);
(*in_back.as_ptr()).back = Some(cur);
} else {
// No prev, we're appending to the front
(*cur.as_ptr()).front = Some(in_back);
(*in_back.as_ptr()).back = Some(cur);
self.list.front = Some(in_front);
}
// Index moves forward by input length
*self.index.as_mut().unwrap() += input.len;
} else if let Some(back) = self.list.back {
// We're on the ghost but non-empty, append to the back
let in_front = input.front.take().unwrap();
let in_back = input.back.take().unwrap();
(*back.as_ptr()).back = Some(in_front);
(*in_front.as_ptr()).front = Some(back);
self.list.back = Some(in_back);
} else {
// We're empty, become the input, remain on the ghost
std::mem::swap(self.list, & mut input);
}
self.list.len += input.len;
// Not necessary but Polite To Do
input.len = 0;
// Input dropped here
< span class = "boring" > }< / span > < / code > < / pre >
< p > 总之，我已经筋疲力尽了，所以 < code > insert< / code > 和 < code > remove< / code > 以及所有其他应用程序接口就留给读者练习。
下面是 Cursor 的最终代码，我做对了吗？我只有在写下一章并测试这个怪东西时才能知道！< / p >
< pre class = "playground" > < code class = "language-rust edition2021" > < span class = "boring" > #![allow(unused)]
< / span > < span class = "boring" > fn main() {
< / span > pub struct CursorMut< 'a, T> {
list: & 'a mut LinkedList< T> ,
cur: Link< T> ,
index: Option< usize> ,
}
impl< T> LinkedList< T> {
pub fn cursor_mut(& mut self) -> CursorMut< T> {
CursorMut {
list: self,
cur: None,
index: None,
}
}
}
impl< 'a, T> CursorMut< 'a, T> {
pub fn index(& self) -> Option< usize> {
self.index
}
pub fn move_next(& mut self) {
if let Some(cur) = self.cur {
unsafe {
// We're on a real element, go to its next (back)
self.cur = (*cur.as_ptr()).back;
if self.cur.is_some() {
*self.index.as_mut().unwrap() += 1;
} else {
// We just walked to the ghost, no more index
self.index = None;
}
}
} else if !self.list.is_empty() {
// We're at the ghost, and there is a real front, so move to it!
self.cur = self.list.front;
self.index = Some(0)
} else {
// We're at the ghost, but that's the only element... do nothing.
}
}
pub fn move_prev(& mut self) {
if let Some(cur) = self.cur {
unsafe {
// We're on a real element, go to its previous (front)
self.cur = (*cur.as_ptr()).front;
if self.cur.is_some() {
*self.index.as_mut().unwrap() -= 1;
} else {
// We just walked to the ghost, no more index
self.index = None;
}
}
} else if !self.list.is_empty() {
// We're at the ghost, and there is a real back, so move to it!
self.cur = self.list.back;
self.index = Some(self.list.len - 1)
} else {
// We're at the ghost, but that's the only element... do nothing.
}
}
pub fn current(& mut self) -> Option< & mut T> {
unsafe {
self.cur.map(|node| & mut (*node.as_ptr()).elem)
}
}
pub fn peek_next(& mut self) -> Option< & mut T> {
unsafe {
self.cur
.and_then(|node| (*node.as_ptr()).back)
.map(|node| & mut (*node.as_ptr()).elem)
}
}
pub fn peek_prev(& mut self) -> Option< & mut T> {
unsafe {
self.cur
.and_then(|node| (*node.as_ptr()).front)
.map(|node| & mut (*node.as_ptr()).elem)
}
}
pub fn split_before(& mut self) -> LinkedList< T> {
// We have this:
//
// list.front -> A < -> B < -> C < -> D < - list.back
// ^
// cur
//
//
// And we want to produce this:
//
// list.front -> C < -> D < - list.back
// ^
// cur
//
//
// return.front -> A < -> B < - return.back
//
if let Some(cur) = self.cur {
// We are pointing at a real element, so the list is non-empty.
unsafe {
// Current state
let old_len = self.list.len;
let old_idx = self.index.unwrap();
let prev = (*cur.as_ptr()).front;
// What self will become
let new_len = old_len - old_idx;
let new_front = self.cur;
let new_back = self.list.back;
let new_idx = Some(0);
// What the output will become
let output_len = old_len - new_len;
let output_front = self.list.front;
let output_back = prev;
// Break the links between cur and prev
if let Some(prev) = prev {
(*cur.as_ptr()).front = None;
(*prev.as_ptr()).back = None;
}
// Produce the result:
self.list.len = new_len;
self.list.front = new_front;
self.list.back = new_back;
self.index = new_idx;
LinkedList {
front: output_front,
back: output_back,
len: output_len,
_boo: PhantomData,
}
}
} else {
// We're at the ghost, just replace our list with an empty one.
// No other state needs to be changed.
std::mem::replace(self.list, LinkedList::new())
}
}
pub fn split_after(& mut self) -> LinkedList< T> {
// We have this:
//
// list.front -> A < -> B < -> C < -> D < - list.back
// ^
// cur
//
//
// And we want to produce this:
//
// list.front -> A < -> B < - list.back
// ^
// cur
//
//
// return.front -> C < -> D < - return.back
//
if let Some(cur) = self.cur {
// We are pointing at a real element, so the list is non-empty.
unsafe {
// Current state
let old_len = self.list.len;
let old_idx = self.index.unwrap();
let next = (*cur.as_ptr()).back;
// What self will become
let new_len = old_idx + 1;
let new_back = self.cur;
let new_front = self.list.front;
let new_idx = Some(old_idx);
// What the output will become
let output_len = old_len - new_len;
let output_front = next;
let output_back = self.list.back;
// Break the links between cur and next
if let Some(next) = next {
(*cur.as_ptr()).back = None;
(*next.as_ptr()).front = None;
}
// Produce the result:
self.list.len = new_len;
self.list.front = new_front;
self.list.back = new_back;
self.index = new_idx;
LinkedList {
front: output_front,
back: output_back,
len: output_len,
_boo: PhantomData,
}
}
} else {
// We're at the ghost, just replace our list with an empty one.
// No other state needs to be changed.
std::mem::replace(self.list, LinkedList::new())
}
}
pub fn splice_before(& mut self, mut input: LinkedList< T> ) {
// We have this:
//
// input.front -> 1 < -> 2 < - input.back
//
// list.front -> A < -> B < -> C < - list.back
// ^
// cur
//
//
// Becoming this:
//
// list.front -> A < -> 1 < -> 2 < -> B < -> C < - list.back
// ^
// cur
//
unsafe {
// We can either `take` the input's pointers or `mem::forget`
// it. Using `take` is more responsible in case we ever do custom
// allocators or something that also needs to be cleaned up!
if input.is_empty() {
// Input is empty, do nothing.
} else if let Some(cur) = self.cur {
// Both lists are non-empty
let in_front = input.front.take().unwrap();
let in_back = input.back.take().unwrap();
if let Some(prev) = (*cur.as_ptr()).front {
// General Case, no boundaries, just internal fixups
(*prev.as_ptr()).back = Some(in_front);
(*in_front.as_ptr()).front = Some(prev);
(*cur.as_ptr()).front = Some(in_back);
(*in_back.as_ptr()).back = Some(cur);
} else {
// No prev, we're appending to the front
(*cur.as_ptr()).front = Some(in_back);
(*in_back.as_ptr()).back = Some(cur);
self.list.front = Some(in_front);
}
// Index moves forward by input length
*self.index.as_mut().unwrap() += input.len;
} else if let Some(back) = self.list.back {
// We're on the ghost but non-empty, append to the back
let in_front = input.front.take().unwrap();
let in_back = input.back.take().unwrap();
(*back.as_ptr()).back = Some(in_front);
(*in_front.as_ptr()).front = Some(back);
self.list.back = Some(in_back);
} else {
// We're empty, become the input, remain on the ghost
std::mem::swap(self.list, & mut input);
}
self.list.len += input.len;
// Not necessary but Polite To Do
input.len = 0;
// Input dropped here
}
}
pub fn splice_after(& mut self, mut input: LinkedList< T> ) {
// We have this:
//
// input.front -> 1 < -> 2 < - input.back
//
// list.front -> A < -> B < -> C < - list.back
// ^
// cur
//
//
// Becoming this:
//
// list.front -> A < -> B < -> 1 < -> 2 < -> C < - list.back
// ^
// cur
//
unsafe {
// We can either `take` the input's pointers or `mem::forget`
// it. Using `take` is more responsible in case we ever do custom
// allocators or something that also needs to be cleaned up!
if input.is_empty() {
// Input is empty, do nothing.
} else if let Some(cur) = self.cur {
// Both lists are non-empty
let in_front = input.front.take().unwrap();
let in_back = input.back.take().unwrap();
if let Some(next) = (*cur.as_ptr()).back {
// General Case, no boundaries, just internal fixups
(*next.as_ptr()).front = Some(in_back);
(*in_back.as_ptr()).back = Some(next);
(*cur.as_ptr()).back = Some(in_front);
(*in_front.as_ptr()).front = Some(cur);
} else {
// No next, we're appending to the back
(*cur.as_ptr()).back = Some(in_front);
(*in_front.as_ptr()).front = Some(cur);
self.list.back = Some(in_back);
}
// Index doesn't change
} else if let Some(front) = self.list.front {
// We're on the ghost but non-empty, append to the front
let in_front = input.front.take().unwrap();
let in_back = input.back.take().unwrap();
(*front.as_ptr()).front = Some(in_back);
(*in_back.as_ptr()).back = Some(front);
self.list.front = Some(in_front);
} else {
// We're empty, become the input, remain on the ghost
std::mem::swap(self.list, & mut input);
}
self.list.len += input.len;
// Not necessary but Polite To Do
input.len = 0;
// Input dropped here
}
}
}
< span class = "boring" > }< / span > < / code > < / pre >
< / main >
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