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<h1 id="filling-in-random-bits"><a class="header" href="#filling-in-random-bits">Filling In Random Bits</a></h1>
<p>嘿,你不是说要做成精品吗?</p>
<p>为了成为一个 &quot;&quot;系列,这里还有一些乱七八糟的东西:</p>
<pre><pre class="playground"><code class="language-rust edition2021"><span class="boring">#![allow(unused)]
</span><span class="boring">fn main() {
</span>impl&lt;T&gt; LinkedList&lt;T&gt; {
pub fn is_empty(&amp;self) -&gt; bool {
self.len == 0
}
pub fn clear(&amp;mut self) {
// Oh look it's drop again
while let Some(_) = self.pop_front() { }
}
}
<span class="boring">}</span></code></pre></pre>
<p>现在,我们已经有了一大堆大家都期待的特性需要实现:</p>
<pre><pre class="playground"><code class="language-rust edition2021"><span class="boring">#![allow(unused)]
</span><span class="boring">fn main() {
</span>impl&lt;T&gt; Default for LinkedList&lt;T&gt; {
fn default() -&gt; Self {
Self::new()
}
}
impl&lt;T: Clone&gt; Clone for LinkedList&lt;T&gt; {
fn clone(&amp;self) -&gt; Self {
let mut new_list = Self::new();
for item in self {
new_list.push_back(item.clone());
}
new_list
}
}
impl&lt;T&gt; Extend&lt;T&gt; for LinkedList&lt;T&gt; {
fn extend&lt;I: IntoIterator&lt;Item = T&gt;&gt;(&amp;mut self, iter: I) {
for item in iter {
self.push_back(item);
}
}
}
impl&lt;T&gt; FromIterator&lt;T&gt; for LinkedList&lt;T&gt; {
fn from_iter&lt;I: IntoIterator&lt;Item = T&gt;&gt;(iter: I) -&gt; Self {
let mut list = Self::new();
list.extend(iter);
list
}
}
impl&lt;T: Debug&gt; Debug for LinkedList&lt;T&gt; {
fn fmt(&amp;self, f: &amp;mut fmt::Formatter&lt;'_&gt;) -&gt; fmt::Result {
f.debug_list().entries(self).finish()
}
}
impl&lt;T: PartialEq&gt; PartialEq for LinkedList&lt;T&gt; {
fn eq(&amp;self, other: &amp;Self) -&gt; bool {
self.len() == other.len() &amp;&amp; self.iter().eq(other)
}
fn ne(&amp;self, other: &amp;Self) -&gt; bool {
self.len() != other.len() || self.iter().ne(other)
}
}
impl&lt;T: Eq&gt; Eq for LinkedList&lt;T&gt; { }
impl&lt;T: PartialOrd&gt; PartialOrd for LinkedList&lt;T&gt; {
fn partial_cmp(&amp;self, other: &amp;Self) -&gt; Option&lt;Ordering&gt; {
self.iter().partial_cmp(other)
}
}
impl&lt;T: Ord&gt; Ord for LinkedList&lt;T&gt; {
fn cmp(&amp;self, other: &amp;Self) -&gt; Ordering {
self.iter().cmp(other)
}
}
impl&lt;T: Hash&gt; Hash for LinkedList&lt;T&gt; {
fn hash&lt;H: Hasher&gt;(&amp;self, state: &amp;mut H) {
self.len().hash(state);
for item in self {
item.hash(state);
}
}
}
<span class="boring">}</span></code></pre></pre>
<p>另一个有趣的话题是哈希本身。你看到我们如何将 <code>len</code> 写入散列的吗?这其实非常重要!如果集合不把 <code>len</code> 加入散列,很可能会意外的造成前缀碰撞。例如,一个集合包含 <code>[&quot;he&quot;, &quot;llo&quot;]</code> 另一个集合包含 <code>[&quot;hello&quot;]</code>,我们该如何区分?如果没有把集合长度或其它&quot;分隔符&quot;加入到散列 ,这将毫无意义!会让意外哈希碰撞发生变得太容易,会导致严重的后果,所以还是照做吧!</p>
<p>好了,这是我们现在的代码:</p>
<pre><pre class="playground"><code class="language-rust edition2021"><span class="boring">#![allow(unused)]
</span><span class="boring">fn main() {
</span>use std::cmp::Ordering;
use std::fmt::{self, Debug};
use std::hash::{Hash, Hasher};
use std::iter::FromIterator;
use std::ptr::NonNull;
use std::marker::PhantomData;
pub struct LinkedList&lt;T&gt; {
front: Link&lt;T&gt;,
back: Link&lt;T&gt;,
len: usize,
_boo: PhantomData&lt;T&gt;,
}
type Link&lt;T&gt; = Option&lt;NonNull&lt;Node&lt;T&gt;&gt;&gt;;
struct Node&lt;T&gt; {
front: Link&lt;T&gt;,
back: Link&lt;T&gt;,
elem: T,
}
pub struct Iter&lt;'a, T&gt; {
front: Link&lt;T&gt;,
back: Link&lt;T&gt;,
len: usize,
_boo: PhantomData&lt;&amp;'a T&gt;,
}
pub struct IterMut&lt;'a, T&gt; {
front: Link&lt;T&gt;,
back: Link&lt;T&gt;,
len: usize,
_boo: PhantomData&lt;&amp;'a mut T&gt;,
}
pub struct IntoIter&lt;T&gt; {
list: LinkedList&lt;T&gt;,
}
impl&lt;T&gt; LinkedList&lt;T&gt; {
pub fn new() -&gt; Self {
Self {
front: None,
back: None,
len: 0,
_boo: PhantomData,
}
}
pub fn push_front(&amp;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.as_ptr()).front = Some(new);
(*new.as_ptr()).back = Some(old);
} else {
// If there's no front, then we're the empty list and need
// to set the back too.
self.back = Some(new);
}
// These things always happen!
self.front = Some(new);
self.len += 1;
}
}
pub fn push_back(&amp;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 {
back: None,
front: None,
elem,
})));
if let Some(old) = self.back {
// Put the new back before the old one
(*old.as_ptr()).back = Some(new);
(*new.as_ptr()).front = Some(old);
} else {
// If there's no back, then we're the empty list and need
// to set the front too.
self.front = Some(new);
}
// These things always happen!
self.back = Some(new);
self.len += 1;
}
}
pub fn pop_front(&amp;mut self) -&gt; Option&lt;T&gt; {
unsafe {
// Only have to do stuff if there is a front node to pop.
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!
self.back = None;
}
self.len -= 1;
result
// Box gets implicitly freed here, knows there is no T.
})
}
}
pub fn pop_back(&amp;mut self) -&gt; Option&lt;T&gt; {
unsafe {
// Only have to do stuff if there is a back node to pop.
self.back.map(|node| {
// Bring the Box front 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 back.
self.back = boxed_node.front;
if let Some(new) = self.back {
// Cleanup its reference to the removed node
(*new.as_ptr()).back = None;
} else {
// If the back is now null, then this list is now empty!
self.front = None;
}
self.len -= 1;
result
// Box gets implicitly freed here, knows there is no T.
})
}
}
pub fn front(&amp;self) -&gt; Option&lt;&amp;T&gt; {
unsafe {
self.front.map(|node| &amp;(*node.as_ptr()).elem)
}
}
pub fn front_mut(&amp;mut self) -&gt; Option&lt;&amp;mut T&gt; {
unsafe {
self.front.map(|node| &amp;mut (*node.as_ptr()).elem)
}
}
pub fn back(&amp;self) -&gt; Option&lt;&amp;T&gt; {
unsafe {
self.back.map(|node| &amp;(*node.as_ptr()).elem)
}
}
pub fn back_mut(&amp;mut self) -&gt; Option&lt;&amp;mut T&gt; {
unsafe {
self.back.map(|node| &amp;mut (*node.as_ptr()).elem)
}
}
pub fn len(&amp;self) -&gt; usize {
self.len
}
pub fn is_empty(&amp;self) -&gt; bool {
self.len == 0
}
pub fn clear(&amp;mut self) {
// Oh look it's drop again
while let Some(_) = self.pop_front() { }
}
pub fn iter(&amp;self) -&gt; Iter&lt;T&gt; {
Iter {
front: self.front,
back: self.back,
len: self.len,
_boo: PhantomData,
}
}
pub fn iter_mut(&amp;mut self) -&gt; IterMut&lt;T&gt; {
IterMut {
front: self.front,
back: self.back,
len: self.len,
_boo: PhantomData,
}
}
pub fn into_iter(self) -&gt; IntoIter&lt;T&gt; {
IntoIter {
list: self
}
}
}
impl&lt;T&gt; Drop for LinkedList&lt;T&gt; {
fn drop(&amp;mut self) {
// Pop until we have to stop
while let Some(_) = self.pop_front() { }
}
}
impl&lt;T&gt; Default for LinkedList&lt;T&gt; {
fn default() -&gt; Self {
Self::new()
}
}
impl&lt;T: Clone&gt; Clone for LinkedList&lt;T&gt; {
fn clone(&amp;self) -&gt; Self {
let mut new_list = Self::new();
for item in self {
new_list.push_back(item.clone());
}
new_list
}
}
impl&lt;T&gt; Extend&lt;T&gt; for LinkedList&lt;T&gt; {
fn extend&lt;I: IntoIterator&lt;Item = T&gt;&gt;(&amp;mut self, iter: I) {
for item in iter {
self.push_back(item);
}
}
}
impl&lt;T&gt; FromIterator&lt;T&gt; for LinkedList&lt;T&gt; {
fn from_iter&lt;I: IntoIterator&lt;Item = T&gt;&gt;(iter: I) -&gt; Self {
let mut list = Self::new();
list.extend(iter);
list
}
}
impl&lt;T: Debug&gt; Debug for LinkedList&lt;T&gt; {
fn fmt(&amp;self, f: &amp;mut fmt::Formatter&lt;'_&gt;) -&gt; fmt::Result {
f.debug_list().entries(self).finish()
}
}
impl&lt;T: PartialEq&gt; PartialEq for LinkedList&lt;T&gt; {
fn eq(&amp;self, other: &amp;Self) -&gt; bool {
self.len() == other.len() &amp;&amp; self.iter().eq(other)
}
fn ne(&amp;self, other: &amp;Self) -&gt; bool {
self.len() != other.len() || self.iter().ne(other)
}
}
impl&lt;T: Eq&gt; Eq for LinkedList&lt;T&gt; { }
impl&lt;T: PartialOrd&gt; PartialOrd for LinkedList&lt;T&gt; {
fn partial_cmp(&amp;self, other: &amp;Self) -&gt; Option&lt;Ordering&gt; {
self.iter().partial_cmp(other)
}
}
impl&lt;T: Ord&gt; Ord for LinkedList&lt;T&gt; {
fn cmp(&amp;self, other: &amp;Self) -&gt; Ordering {
self.iter().cmp(other)
}
}
impl&lt;T: Hash&gt; Hash for LinkedList&lt;T&gt; {
fn hash&lt;H: Hasher&gt;(&amp;self, state: &amp;mut H) {
self.len().hash(state);
for item in self {
item.hash(state);
}
}
}
impl&lt;'a, T&gt; IntoIterator for &amp;'a LinkedList&lt;T&gt; {
type IntoIter = Iter&lt;'a, T&gt;;
type Item = &amp;'a T;
fn into_iter(self) -&gt; Self::IntoIter {
self.iter()
}
}
impl&lt;'a, T&gt; Iterator for Iter&lt;'a, T&gt; {
type Item = &amp;'a T;
fn next(&amp;mut self) -&gt; Option&lt;Self::Item&gt; {
// While self.front == self.back is a tempting condition to check here,
// it won't do the right for yielding the last element! That sort of
// thing only works for arrays because of &quot;one-past-the-end&quot; pointers.
if self.len &gt; 0 {
// We could unwrap front, but this is safer and easier
self.front.map(|node| unsafe {
self.len -= 1;
self.front = (*node.as_ptr()).back;
&amp;(*node.as_ptr()).elem
})
} else {
None
}
}
fn size_hint(&amp;self) -&gt; (usize, Option&lt;usize&gt;) {
(self.len, Some(self.len))
}
}
impl&lt;'a, T&gt; DoubleEndedIterator for Iter&lt;'a, T&gt; {
fn next_back(&amp;mut self) -&gt; Option&lt;Self::Item&gt; {
if self.len &gt; 0 {
self.back.map(|node| unsafe {
self.len -= 1;
self.back = (*node.as_ptr()).front;
&amp;(*node.as_ptr()).elem
})
} else {
None
}
}
}
impl&lt;'a, T&gt; ExactSizeIterator for Iter&lt;'a, T&gt; {
fn len(&amp;self) -&gt; usize {
self.len
}
}
impl&lt;'a, T&gt; IntoIterator for &amp;'a mut LinkedList&lt;T&gt; {
type IntoIter = IterMut&lt;'a, T&gt;;
type Item = &amp;'a mut T;
fn into_iter(self) -&gt; Self::IntoIter {
self.iter_mut()
}
}
impl&lt;'a, T&gt; Iterator for IterMut&lt;'a, T&gt; {
type Item = &amp;'a mut T;
fn next(&amp;mut self) -&gt; Option&lt;Self::Item&gt; {
// While self.front == self.back is a tempting condition to check here,
// it won't do the right for yielding the last element! That sort of
// thing only works for arrays because of &quot;one-past-the-end&quot; pointers.
if self.len &gt; 0 {
// We could unwrap front, but this is safer and easier
self.front.map(|node| unsafe {
self.len -= 1;
self.front = (*node.as_ptr()).back;
&amp;mut (*node.as_ptr()).elem
})
} else {
None
}
}
fn size_hint(&amp;self) -&gt; (usize, Option&lt;usize&gt;) {
(self.len, Some(self.len))
}
}
impl&lt;'a, T&gt; DoubleEndedIterator for IterMut&lt;'a, T&gt; {
fn next_back(&amp;mut self) -&gt; Option&lt;Self::Item&gt; {
if self.len &gt; 0 {
self.back.map(|node| unsafe {
self.len -= 1;
self.back = (*node.as_ptr()).front;
&amp;mut (*node.as_ptr()).elem
})
} else {
None
}
}
}
impl&lt;'a, T&gt; ExactSizeIterator for IterMut&lt;'a, T&gt; {
fn len(&amp;self) -&gt; usize {
self.len
}
}
impl&lt;T&gt; IntoIterator for LinkedList&lt;T&gt; {
type IntoIter = IntoIter&lt;T&gt;;
type Item = T;
fn into_iter(self) -&gt; Self::IntoIter {
self.into_iter()
}
}
impl&lt;T&gt; Iterator for IntoIter&lt;T&gt; {
type Item = T;
fn next(&amp;mut self) -&gt; Option&lt;Self::Item&gt; {
self.list.pop_front()
}
fn size_hint(&amp;self) -&gt; (usize, Option&lt;usize&gt;) {
(self.list.len, Some(self.list.len))
}
}
impl&lt;T&gt; DoubleEndedIterator for IntoIter&lt;T&gt; {
fn next_back(&amp;mut self) -&gt; Option&lt;Self::Item&gt; {
self.list.pop_back()
}
}
impl&lt;T&gt; ExactSizeIterator for IntoIter&lt;T&gt; {
fn len(&amp;self) -&gt; usize {
self.list.len
}
}
#[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);
}
}
<span class="boring">}</span></code></pre></pre>
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