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<main>
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<h1 id="implementing-cursors"><a class="header" href="#implementing-cursors">Implementing Cursors</a></h1>
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<p>好了，我们现在讨论 CursorMut。就像我最初的设计一样，它有一个包含 None 的 “幽灵 “元素，用来指示列表的开始/结束，你可以 “跨过它”，绕到列表的另一边。要实现它，我们需要</p>
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<ul>
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<li>指向当前节点的指针</li>
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<li>指向列表的指针</li>
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<li>当前索引</li>
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</ul>
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<p>等等，当我们指向 “幽灵 “时，索引是多少？</p>
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<p>好吧，游标 (cursors)上的索引返回一个 <code>Option<usize></code>，这很合理。Std 的实现做了一堆垃圾来避免将其存储为一个 Option，但是…… 我们是一个链接列表，这很好。此外，std 还有 cursor_front/cursor_back 功能，它可以在前/后元素上启动光标，感觉很直观，但当列表为空时，又要做一些奇怪的事情。</p>
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<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>
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<p>让我们开始吧：</p>
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<p>非常简单直接，上面的需求列表每一项都有一个字段！</p>
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<pre class="playground"><code class="language-rust edition2021"><span class="boring">#![allow(unused)]
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</span><span class="boring">fn main() {
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</span>pub struct CursorMut<'a, T> {
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cur: Link<T>,
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list: &'a mut LinkedList<T>,
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index: Option<usize>,
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}
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|
|
<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，它们会将当前元素之前/之后的所有内容以 LinkedList 的形式返回（在幽灵元素处停止，在这种情况下，我们只返回整个 List，光标现在指向一个空 list）：</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”，所以没什么可更新的。不错。哦，嘿嘿，这在第四种情况下也对！</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，我估计这是最容易出错的一个。这两个函数接收一个 LinkedList，并将其内容嫁接到我们的列表中。我们的列表可能是空的，他们的列表也可能是空的，我们还有幽灵节点要处理……叹口气，让我们一步一步来吧，从 splice_before 开始。</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（0），则追加到前面（更改 list.front）</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’re empty” 中有以下错误。所以我们应该使用 <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，下面的代码存在bug：</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>！boom，panic！</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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