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<ol class="chapter"><li class="chapter-item affix "><a href="../../about-book.html">关于本书</a></li><li class="chapter-item affix "><a href="../../into-rust.html">进入 Rust 编程世界</a></li><li class="chapter-item affix "><a href="../../first-try/sth-you-should-not-do.html">避免从入门到放弃</a></li><li class="chapter-item affix "><a href="../../community.html">社区和锈书</a></li><li class="spacer"></li><li class="chapter-item affix "><a href="../../some-thoughts.html">Xobserve: 一切皆可观测</a></li><li class="chapter-item affix "><a href="../../beat-ai.html">BeatAI: 工程师 AI 入门圣经</a></li><li class="chapter-item affix "><li class="part-title">Rust 语言基础学习</li><li class="spacer"></li><li class="chapter-item "><a href="../../first-try/intro.html"><strong aria-hidden="true">1.</strong> 寻找牛刀，以便小试</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../../first-try/installation.html"><strong aria-hidden="true">1.1.</strong> 安装 Rust 环境</a></li><li class="chapter-item "><a href="../../first-try/editor.html"><strong aria-hidden="true">1.2.</strong> 墙推 VSCode!</a></li><li class="chapter-item "><a href="../../first-try/cargo.html"><strong aria-hidden="true">1.3.</strong> 认识 Cargo</a></li><li class="chapter-item "><a href="../../first-try/hello-world.html"><strong aria-hidden="true">1.4.</strong> 不仅仅是 Hello world</a></li><li class="chapter-item "><a href="../../first-try/slowly-downloading.html"><strong aria-hidden="true">1.5.</strong> 下载依赖太慢了？</a></li></ol></li><li class="chapter-item "><a href="../../basic/intro.html"><strong aria-hidden="true">2.</strong> Rust 基础入门</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../../basic/variable.html"><strong aria-hidden="true">2.1.</strong> 变量绑定与解构</a></li><li class="chapter-item "><a href="../../basic/base-type/index.html"><strong aria-hidden="true">2.2.</strong> 基本类型</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../../basic/base-type/numbers.html"><strong aria-hidden="true">2.2.1.</strong> 数值类型</a></li><li class="chapter-item "><a href="../../basic/base-type/char-bool.html"><strong aria-hidden="true">2.2.2.</strong> 字符、布尔、单元类型</a></li><li class="chapter-item "><a href="../../basic/base-type/statement-expression.html"><strong aria-hidden="true">2.2.3.</strong> 语句与表达式</a></li><li class="chapter-item "><a href="../../basic/base-type/function.html"><strong aria-hidden="true">2.2.4.</strong> 函数</a></li></ol></li><li class="chapter-item "><a href="../../basic/ownership/index.html"><strong aria-hidden="true">2.3.</strong> 所有权和借用</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../../basic/ownership/ownership.html"><strong aria-hidden="true">2.3.1.</strong> 所有权</a></li><li class="chapter-item "><a href="../../basic/ownership/borrowing.html"><strong aria-hidden="true">2.3.2.</strong> 引用与借用</a></li></ol></li><li class="chapter-item "><a href="../../basic/compound-type/intro.html"><strong aria-hidden="true">2.4.</strong> 复合类型</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../../basic/compound-type/string-slice.html"><strong aria-hidden="true">2.4.1.</strong> 字符串与切片</a></li><li class="chapter-item "><a href="../../basic/compound-type/tuple.html"><strong aria-hidden="true">2.4.2.</strong> 元组</a></li><li class="chapter-item "><a href="../../basic/compound-type/struct.html"><strong aria-hidden="true">2.4.3.</strong> 结构体</a></li><li class="chapter-item "><a href="../../basic/compound-type/enum.html"><strong aria-hidden="true">2.4.4.</strong> 枚举</a></li><li class="chapter-item "><a href="../../basic/compound-type/array.html"><strong aria-hidden="true">2.4.5.</strong> 数组</a></l
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<main>
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<h1 id="数据布局和基本操作"><a class="header" href="#数据布局和基本操作">数据布局和基本操作</a></h1>
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<p>对于新的链表来说，最重要的就是我们可以自由地操控列表的尾部( tail )。</p>
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<h2 id="数据布局"><a class="header" href="#数据布局">数据布局</a></h2>
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<p>例如以下是一个不太常见的持久化列表布局:</p>
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<pre><code class="language-shell">list1 = A -> B -> C -> D
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list2 = tail(list1) = B -> C -> D
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list3 = push(list2, X) = X -> B -> C -> D
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</code></pre>
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<p>如果上面的不够清晰，我们还可以从内存角度来看：</p>
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<pre><code class="language-shell">list1 -> A ---+
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v
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list2 ------> B -> C -> D
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^
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list3 -> X ---+
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</code></pre>
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<p>这里大家可能会看出一些端倪：节点 <code>B</code> 被多个链表所共享，这造成了我们无法通过 <code>Box</code> 的方式来实现，因为如果使用 <code>Box</code>，还存在一个问题，谁来负责清理释放？如果 drop <code>list2</code>，那 <code>B</code> 节点会被清理释放吗？</p>
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<p>函数式语言或者说其它绝大多数语言，并不存在这个问题，因为 GC 垃圾回收解千愁，但是 Rust 并没有。</p>
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<p>好在标准库为我们提供了引用计数的数据结构: <code>Rc / Arc</code>，引用计数可以被认为是一种简单的 GC，对于很多场景来说，引用计数的数据吞吐量要远小于垃圾回收，而且引用计数还存在循环引用的风险！但... 我们有其它选择吗？ :(</p>
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<p>不过使用 Rc 意味着我们的数据将无法被改变，因为它不具备内部可变性，关于 Rc/Arc 的详细介绍请看<a href="https://course.rs/advance/smart-pointer/rc-arc.html">这里</a>。</p>
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<p>下面，简单的将我们的数据结构通过 <code>Rc</code> 来实现：</p>
|
|
|
|
|
|
<pre><pre class="playground"><code class="language-rust edition2021"><span class="boring">#![allow(unused)]
|
|
|
|
|
|
</span><span class="boring">fn main() {
|
|
|
|
|
|
</span>// in third.rs
|
|
|
|
|
|
use std::rc::Rc;
|
|
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|
|
|
|
|
|
|
|
|
pub struct List<T> {
|
|
|
|
|
|
head: Link<T>,
|
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|
|
}
|
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|
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|
type Link<T> = Option<Rc<Node<T>>>;
|
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|
|
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|
|
|
|
|
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struct Node<T> {
|
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elem: T,
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|
|
|
next: Link<T>,
|
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|
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|
}
|
|
|
|
|
|
<span class="boring">}</span></code></pre></pre>
|
|
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|
|
|
<p>需要注意的是, <code>Rc</code> 在 Rust 中并不是一等公民，它没有被包含在 <code>std::prelude</code> 中，因此我们必须手动引入 <code>use std::rc::Rc</code> (混得好失败 - , -)</p>
|
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|
<h2 id="基本操作"><a class="header" href="#基本操作">基本操作</a></h2>
|
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|
|
<p>首先，对于 List 的构造器，可以直接复制粘贴:</p>
|
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|
|
<pre><pre class="playground"><code class="language-rust edition2021"><span class="boring">#![allow(unused)]
|
|
|
|
|
|
</span><span class="boring">fn main() {
|
|
|
|
|
|
</span>impl<T> List<T> {
|
|
|
|
|
|
pub fn new() -> Self {
|
|
|
|
|
|
List { head: None }
|
|
|
|
|
|
}
|
|
|
|
|
|
}
|
|
|
|
|
|
<span class="boring">}</span></code></pre></pre>
|
|
|
|
|
|
<p>而之前的 <code>push</code> 和 <code>pop</code> 已无任何意义，因为新链表是不可变的，但我们可以使用功能相似的 <code>prepend</code> 和 <code>tail</code> 来返回新的链表。</p>
|
|
|
|
|
|
<pre><pre class="playground"><code class="language-rust edition2021"><span class="boring">#![allow(unused)]
|
|
|
|
|
|
</span><span class="boring">fn main() {
|
|
|
|
|
|
</span>pub fn prepend(&self, elem: T) -> List<T> {
|
|
|
|
|
|
List { head: Some(Rc::new(Node {
|
|
|
|
|
|
elem: elem,
|
|
|
|
|
|
next: self.head.clone(),
|
|
|
|
|
|
}))}
|
|
|
|
|
|
}
|
|
|
|
|
|
<span class="boring">}</span></code></pre></pre>
|
|
|
|
|
|
<p>大家可能会大惊失色，什么，你竟然用了 <code>clone</code>，不是号称高性能链表实现吗？别急，这里其实只是 <code>Rc::clone</code>，对于该方法而言，<code>clone</code> 仅仅是增加引用计数，并不是复制底层的数据。虽然 <code>Rc</code> 的性能要比 <code>Box</code> 的引用方式低一点，但是它依然是多所有权前提下最好的解决方式或者说之一。</p>
|
|
|
|
|
|
<p>还有一点值得注意， <code>head</code> 是 <code>Option<Rc<Node<T>>></code> 类型，那么为何不先匹配出内部的 <code>Rc<Node<T>></code>，然后再 clone 呢？原因是 <code>Option</code> 也提供了相应的 API，它的功能跟我们的需求是一致的。</p>
|
|
|
|
|
|
<p>运行下试试：</p>
|
|
|
|
|
|
<pre><code class="language-shell">$ cargo build
|
|
|
|
|
|
|
|
|
|
|
|
warning: field is never used: `elem`
|
|
|
|
|
|
--> src/third.rs:10:5
|
|
|
|
|
|
|
|
|
|
|
|
|
10 | elem: T,
|
|
|
|
|
|
| ^^^^^^^
|
|
|
|
|
|
|
|
|
|
|
|
|
= note: #[warn(dead_code)] on by default
|
|
|
|
|
|
|
|
|
|
|
|
warning: field is never used: `next`
|
|
|
|
|
|
--> src/third.rs:11:5
|
|
|
|
|
|
|
|
|
|
|
|
|
11 | next: Link<T>,
|
|
|
|
|
|
| ^^^^^^^^^^^^^
|
|
|
|
|
|
</code></pre>
|
|
|
|
|
|
<p>胆战心惊的编译通过(胆战心惊? 日常基本操作，请坐下!)。</p>
|
|
|
|
|
|
<p>继续来实现 <code>tail</code>，该方法会将现有链表的首个元素移除，并返回剩余的链表:</p>
|
|
|
|
|
|
<pre><pre class="playground"><code class="language-rust edition2021"><span class="boring">#![allow(unused)]
|
|
|
|
|
|
</span><span class="boring">fn main() {
|
|
|
|
|
|
</span>pub fn tail(&self) -> List<T> {
|
|
|
|
|
|
List { head: self.head.as_ref().map(|node| node.next.clone()) }
|
|
|
|
|
|
}
|
|
|
|
|
|
<span class="boring">}</span></code></pre></pre>
|
|
|
|
|
|
<pre><code class="language-shell">$ cargo build
|
|
|
|
|
|
|
|
|
|
|
|
error[E0308]: mismatched types
|
|
|
|
|
|
--> src/third.rs:27:22
|
|
|
|
|
|
|
|
|
|
|
|
|
27 | List { head: self.head.as_ref().map(|node| node.next.clone()) }
|
|
|
|
|
|
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected struct `std::rc::Rc`, found enum `std::option::Option`
|
|
|
|
|
|
|
|
|
|
|
|
|
= note: expected type `std::option::Option<std::rc::Rc<_>>`
|
|
|
|
|
|
found type `std::option::Option<std::option::Option<std::rc::Rc<_>>>`
|
|
|
|
|
|
</code></pre>
|
|
|
|
|
|
<p>看起来这里的 <code>map</code> 多套了一层 <code>Option</code>，可以用 <code>and_then</code> 替代：</p>
|
|
|
|
|
|
<pre><pre class="playground"><code class="language-rust edition2021"><span class="boring">#![allow(unused)]
|
|
|
|
|
|
</span><span class="boring">fn main() {
|
|
|
|
|
|
</span>pub fn tail(&self) -> List<T> {
|
|
|
|
|
|
List { head: self.head.as_ref().and_then(|node| node.next.clone()) }
|
|
|
|
|
|
}
|
|
|
|
|
|
<span class="boring">}</span></code></pre></pre>
|
|
|
|
|
|
<p>顺利通过编译，很棒！最后就是实现 <code>head</code> 方法，它返回首个元素的引用，跟之前链表的 <code>peek</code> 方法一样:</p>
|
|
|
|
|
|
<pre><pre class="playground"><code class="language-rust edition2021"><span class="boring">#![allow(unused)]
|
|
|
|
|
|
</span><span class="boring">fn main() {
|
|
|
|
|
|
</span>pub fn head(&self) -> Option<&T> {
|
|
|
|
|
|
self.head.as_ref().map(|node| &node.elem )
|
|
|
|
|
|
}
|
|
|
|
|
|
<span class="boring">}</span></code></pre></pre>
|
|
|
|
|
|
<p>好了，至此，新链表的基本操作都已经实现，最后让我们写几个测试用例来看看它们是骡子还是马：</p>
|
|
|
|
|
|
<pre><pre class="playground"><code class="language-rust edition2021"><span class="boring">#![allow(unused)]
|
|
|
|
|
|
</span><span class="boring">fn main() {
|
|
|
|
|
|
</span>#[cfg(test)]
|
|
|
|
|
|
mod test {
|
|
|
|
|
|
use super::List;
|
|
|
|
|
|
|
|
|
|
|
|
#[test]
|
|
|
|
|
|
fn basics() {
|
|
|
|
|
|
let list = List::new();
|
|
|
|
|
|
assert_eq!(list.head(), None);
|
|
|
|
|
|
|
|
|
|
|
|
let list = list.prepend(1).prepend(2).prepend(3);
|
|
|
|
|
|
assert_eq!(list.head(), Some(&3));
|
|
|
|
|
|
|
|
|
|
|
|
let list = list.tail();
|
|
|
|
|
|
assert_eq!(list.head(), Some(&2));
|
|
|
|
|
|
|
|
|
|
|
|
let list = list.tail();
|
|
|
|
|
|
assert_eq!(list.head(), Some(&1));
|
|
|
|
|
|
|
|
|
|
|
|
let list = list.tail();
|
|
|
|
|
|
assert_eq!(list.head(), None);
|
|
|
|
|
|
|
|
|
|
|
|
// Make sure empty tail works
|
|
|
|
|
|
let list = list.tail();
|
|
|
|
|
|
assert_eq!(list.head(), None);
|
|
|
|
|
|
|
|
|
|
|
|
}
|
|
|
|
|
|
}
|
|
|
|
|
|
<span class="boring">}</span></code></pre></pre>
|
|
|
|
|
|
<pre><code class="language-shell">$ cargo test
|
|
|
|
|
|
|
|
|
|
|
|
Running target/debug/lists-5c71138492ad4b4a
|
|
|
|
|
|
|
|
|
|
|
|
running 5 tests
|
|
|
|
|
|
test first::test::basics ... ok
|
|
|
|
|
|
test second::test::into_iter ... ok
|
|
|
|
|
|
test second::test::basics ... ok
|
|
|
|
|
|
test second::test::iter ... ok
|
|
|
|
|
|
test third::test::basics ... ok
|
|
|
|
|
|
|
|
|
|
|
|
test result: ok. 5 passed; 0 failed; 0 ignored; 0 measured
|
|
|
|
|
|
</code></pre>
|
|
|
|
|
|
<p>哦对了... 我们好像忘了一个重要特性：对链表的迭代。</p>
|
|
|
|
|
|
<pre><pre class="playground"><code class="language-rust edition2021"><span class="boring">#![allow(unused)]
|
|
|
|
|
|
</span><span class="boring">fn main() {
|
|
|
|
|
|
</span>pub struct Iter<'a, T> {
|
|
|
|
|
|
next: Option<&'a Node<T>>,
|
|
|
|
|
|
}
|
|
|
|
|
|
|
|
|
|
|
|
impl<T> List<T> {
|
|
|
|
|
|
pub fn iter(&self) -> Iter<'_, T> {
|
|
|
|
|
|
Iter { next: self.head.as_deref() }
|
|
|
|
|
|
}
|
|
|
|
|
|
}
|
|
|
|
|
|
|
|
|
|
|
|
impl<'a, T> Iterator for Iter<'a, T> {
|
|
|
|
|
|
type Item = &'a T;
|
|
|
|
|
|
|
|
|
|
|
|
fn next(&mut self) -> Option<Self::Item> {
|
|
|
|
|
|
self.next.map(|node| {
|
|
|
|
|
|
self.next = node.next.as_deref();
|
|
|
|
|
|
&node.elem
|
|
|
|
|
|
})
|
|
|
|
|
|
}
|
|
|
|
|
|
}
|
|
|
|
|
|
<span class="boring">}</span></code></pre></pre>
|
|
|
|
|
|
<pre><pre class="playground"><code class="language-rust edition2021"><span class="boring">#![allow(unused)]
|
|
|
|
|
|
</span><span class="boring">fn main() {
|
|
|
|
|
|
</span>#[test]
|
|
|
|
|
|
fn iter() {
|
|
|
|
|
|
let list = List::new().prepend(1).prepend(2).prepend(3);
|
|
|
|
|
|
|
|
|
|
|
|
let mut iter = list.iter();
|
|
|
|
|
|
assert_eq!(iter.next(), Some(&3));
|
|
|
|
|
|
assert_eq!(iter.next(), Some(&2));
|
|
|
|
|
|
assert_eq!(iter.next(), Some(&1));
|
|
|
|
|
|
}
|
|
|
|
|
|
<span class="boring">}</span></code></pre></pre>
|
|
|
|
|
|
<pre><code class="language-shell">$ cargo test
|
|
|
|
|
|
|
|
|
|
|
|
Running target/debug/lists-5c71138492ad4b4a
|
|
|
|
|
|
|
|
|
|
|
|
running 7 tests
|
|
|
|
|
|
test first::test::basics ... ok
|
|
|
|
|
|
test second::test::basics ... ok
|
|
|
|
|
|
test second::test::iter ... ok
|
|
|
|
|
|
test second::test::into_iter ... ok
|
|
|
|
|
|
test second::test::peek ... ok
|
|
|
|
|
|
test third::test::basics ... ok
|
|
|
|
|
|
test third::test::iter ... ok
|
|
|
|
|
|
|
|
|
|
|
|
test result: ok. 6 passed; 0 failed; 0 ignored; 0 measured
|
|
|
|
|
|
</code></pre>
|
|
|
|
|
|
<p>细心的同学可能会觉得我在凑字数，这不跟之前的链表迭代实现一样一样的嘛？恭喜你答对了 ：）</p>
|
|
|
|
|
|
<p>最后，给大家留个作业，你可以尝试下看能不能实现 <code>IntoIter</code> 和 <code>IterMut</code>，如果实现不了请不要打我，冤有头债有主，都是 <code>Rc</code> 惹的祸 :(</p>
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</html>
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