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<main>
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<h1 id="basics"><a class="header" href="#basics">Basics</a></h1>
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<p>好了，这就是本书最烂的部分，也是我花了 7 年时间才写完这一章的原因！是时候把我们已经做过 5 次的枯燥乏味的东西再写一遍了，但因为我们必须使用 <code>Option<NonNull<Node<T>></code> 把每件事都做两遍，所以显得格外冗长！</p>
|
|
|
<pre><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 new() -> Self {
|
|
|
Self {
|
|
|
front: None,
|
|
|
back: None,
|
|
|
len: 0,
|
|
|
_boo: PhantomData,
|
|
|
}
|
|
|
}
|
|
|
}
|
|
|
<span class="boring">}</span></code></pre></pre>
|
|
|
<p>PhantomData 是一种奇怪的类型，没有字段，所以你只需说出它的类型名称就能创建一个。</p>
|
|
|
<pre><pre class="playground"><code class="language-rust edition2021"><span class="boring">#![allow(unused)]
|
|
|
</span><span class="boring">fn main() {
|
|
|
</span>pub fn push_front(&mut self, elem: T) {
|
|
|
// SAFETY: it's a linked-list, what do you want?
|
|
|
unsafe {
|
|
|
let new = NonNull::new_unchecked(Box::into_raw(Box::new(Node {
|
|
|
front: None,
|
|
|
back: None,
|
|
|
elem,
|
|
|
})));
|
|
|
if let Some(old) = self.front {
|
|
|
// Put the new front before the old one
|
|
|
(*old).front = Some(new);
|
|
|
(*new).back = Some(old);
|
|
|
} else {
|
|
|
// If there's no front, then we're the empty list and need
|
|
|
// to set the back too. Also here's some integrity checks
|
|
|
// for testing, in case we mess up.
|
|
|
debug_assert!(self.back.is_none());
|
|
|
debug_assert!(self.front.is_none());
|
|
|
debug_assert!(self.len == 0);
|
|
|
self.back = Some(new);
|
|
|
}
|
|
|
self.front = Some(new);
|
|
|
self.len += 1;
|
|
|
}
|
|
|
}
|
|
|
error[E0614]: type `NonNull<Node<T>>` cannot be dereferenced
|
|
|
--> src\lib.rs:39:17
|
|
|
|
|
|
|
39 | (*old).front = Some(new);
|
|
|
| ^^^^^^
|
|
|
<span class="boring">}</span></code></pre></pre>
|
|
|
<p>是的，我真恨 <code>NonNull<Node<T>></code>。我们需要明确地使用 <code>as_ptr</code> 从 NonNull 中获取原始指针，因为 DerefMut 是以 <code>&mut</code> 定义的，我们不想在不安全代码中随意引入安全引用！</p>
|
|
|
<pre><pre class="playground"><code class="language-rust edition2021"><span class="boring">#![allow(unused)]
|
|
|
</span><span class="boring">fn main() {
|
|
|
</span> (*old.as_ptr()).front = Some(new);
|
|
|
(*new.as_ptr()).back = Some(old);
|
|
|
Compiling linked-list v0.0.3
|
|
|
warning: field is never read: `elem`
|
|
|
--> src\lib.rs:16:5
|
|
|
|
|
|
|
16 | elem: T,
|
|
|
| ^^^^^^^
|
|
|
|
|
|
|
= note: `#[warn(dead_code)]` on by default
|
|
|
|
|
|
warning: `linked-list` (lib) generated 1 warning (1 duplicate)
|
|
|
warning: `linked-list` (lib test) generated 1 warning
|
|
|
Finished test [unoptimized + debuginfo] target(s) in 0.33s
|
|
|
<span class="boring">}</span></code></pre></pre>
|
|
|
<p>很好，接下来是 <code>pop</code> 和 <code>len</code>：</p>
|
|
|
<pre><pre class="playground"><code class="language-rust edition2021"><span class="boring">#![allow(unused)]
|
|
|
</span><span class="boring">fn main() {
|
|
|
</span>pub fn pop_front(&mut self) -> Option<T> {
|
|
|
unsafe {
|
|
|
// Only have to do stuff if there is a front node to pop.
|
|
|
// Note that we don't need to mess around with `take` anymore
|
|
|
// because everything is Copy and there are no dtors that will
|
|
|
// run if we mess up... right? :) Riiiight? :)))
|
|
|
self.front.map(|node| {
|
|
|
// Bring the Box back to life so we can move out its value and
|
|
|
// Drop it (Box continues to magically understand this for us).
|
|
|
let boxed_node = Box::from_raw(node.as_ptr());
|
|
|
let result = boxed_node.elem;
|
|
|
|
|
|
// Make the next node into the new front.
|
|
|
self.front = boxed_node.back;
|
|
|
if let Some(new) = self.front {
|
|
|
// Cleanup its reference to the removed node
|
|
|
(*new.as_ptr()).front = None;
|
|
|
} else {
|
|
|
// If the front is now null, then this list is now empty!
|
|
|
debug_assert!(self.len == 1);
|
|
|
self.back = None;
|
|
|
}
|
|
|
|
|
|
self.len -= 1;
|
|
|
result
|
|
|
// Box gets implicitly freed here, knows there is no T.
|
|
|
})
|
|
|
}
|
|
|
}
|
|
|
|
|
|
pub fn len(&self) -> usize {
|
|
|
self.len
|
|
|
}
|
|
|
Compiling linked-list v0.0.3
|
|
|
Finished dev [unoptimized + debuginfo] target(s) in 0.37s
|
|
|
<span class="boring">}</span></code></pre></pre>
|
|
|
<p>在我看来是合法的，是时候写一个测试了！</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::LinkedList;
|
|
|
|
|
|
#[test]
|
|
|
fn test_basic_front() {
|
|
|
let mut list = LinkedList::new();
|
|
|
|
|
|
// Try to break an empty list
|
|
|
assert_eq!(list.len(), 0);
|
|
|
assert_eq!(list.pop_front(), None);
|
|
|
assert_eq!(list.len(), 0);
|
|
|
|
|
|
// Try to break a one item list
|
|
|
list.push_front(10);
|
|
|
assert_eq!(list.len(), 1);
|
|
|
assert_eq!(list.pop_front(), Some(10));
|
|
|
assert_eq!(list.len(), 0);
|
|
|
assert_eq!(list.pop_front(), None);
|
|
|
assert_eq!(list.len(), 0);
|
|
|
|
|
|
// Mess around
|
|
|
list.push_front(10);
|
|
|
assert_eq!(list.len(), 1);
|
|
|
list.push_front(20);
|
|
|
assert_eq!(list.len(), 2);
|
|
|
list.push_front(30);
|
|
|
assert_eq!(list.len(), 3);
|
|
|
assert_eq!(list.pop_front(), Some(30));
|
|
|
assert_eq!(list.len(), 2);
|
|
|
list.push_front(40);
|
|
|
assert_eq!(list.len(), 3);
|
|
|
assert_eq!(list.pop_front(), Some(40));
|
|
|
assert_eq!(list.len(), 2);
|
|
|
assert_eq!(list.pop_front(), Some(20));
|
|
|
assert_eq!(list.len(), 1);
|
|
|
assert_eq!(list.pop_front(), Some(10));
|
|
|
assert_eq!(list.len(), 0);
|
|
|
assert_eq!(list.pop_front(), None);
|
|
|
assert_eq!(list.len(), 0);
|
|
|
assert_eq!(list.pop_front(), None);
|
|
|
assert_eq!(list.len(), 0);
|
|
|
}
|
|
|
}
|
|
|
Compiling linked-list v0.0.3
|
|
|
Finished test [unoptimized + debuginfo] target(s) in 0.40s
|
|
|
Running unittests src\lib.rs
|
|
|
|
|
|
running 1 test
|
|
|
test test::test_basic_front ... ok
|
|
|
|
|
|
test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s
|
|
|
<span class="boring">}</span></code></pre></pre>
|
|
|
<p>万幸，我们是完美的！是吗？</p>
|
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