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<main>
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<h1 id="boring-combinatorics"><a class="header" href="#boring-combinatorics">Boring Combinatorics</a></h1>
|
|
|
<p>好了，回到我们的常规链接列表！</p>
|
|
|
<p>首先，让我们来解决 <code>Drop</code> 的问题：</p>
|
|
|
<pre><pre class="playground"><code class="language-rust edition2021"><span class="boring">#![allow(unused)]
|
|
|
</span><span class="boring">fn main() {
|
|
|
</span>impl<T> Drop for LinkedList<T> {
|
|
|
fn drop(&mut self) {
|
|
|
// Pop until we have to stop
|
|
|
while let Some(_) = self.pop_front() { }
|
|
|
}
|
|
|
}
|
|
|
<span class="boring">}</span></code></pre></pre>
|
|
|
<p>我们必须填写一堆非常无聊的组合实现，如 front、front_mut、back、back_mut、iter、iter_mut、into_iter......</p>
|
|
|
<p>我已经精心设计了之前的 push/pop 实现，因此我们只需前后对调，代码就能做正确的事情！痛苦的经验万岁！(对于节点来说，使用 "prev和next "是很有诱惑力的，但我发现，为了避免错误，尽量使用 "front "和 "back"才是真正对的）。</p>
|
|
|
<p>首先是 <code>front</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 front(&self) -> Option<&T> {
|
|
|
unsafe {
|
|
|
self.front.map(|node| &(*node.as_ptr()).elem)
|
|
|
}
|
|
|
}
|
|
|
<span class="boring">}</span></code></pre></pre>
|
|
|
<p>接着是：</p>
|
|
|
<pre><pre class="playground"><code class="language-rust edition2021"><span class="boring">#![allow(unused)]
|
|
|
</span><span class="boring">fn main() {
|
|
|
</span>pub fn front_mut(&mut self) -> Option<&mut T> {
|
|
|
unsafe {
|
|
|
self.front.map(|node| &mut (*node.as_ptr()).elem)
|
|
|
}
|
|
|
}
|
|
|
<span class="boring">}</span></code></pre></pre>
|
|
|
<p>我会把所有的 <code>back</code> 版本放到文章最终的代码中。</p>
|
|
|
<p>接下来是迭代器。与之前的所有列表不同，我们终于解锁了双端迭代器（<a href="https://doc.rust-lang.org/std/iter/trait.DoubleEndedIterator.html">DoubleEndedIterator</a>）的功能，而且如果要达到生产质量，我们还要支持精确大小迭代器（ <a href="https://doc.rust-lang.org/std/iter/trait.ExactSizeIterator.html">ExactSizeIterator</a>）。</p>
|
|
|
<p>因此，除了 <code>next</code> 和 <code>size_hint</code>，我们还将支持 <code>next_back</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 struct Iter<'a, T> {
|
|
|
front: Link<T>,
|
|
|
back: Link<T>,
|
|
|
len: usize,
|
|
|
_boo: PhantomData<&'a T>,
|
|
|
}
|
|
|
|
|
|
impl<T> LinkedList<T> {
|
|
|
pub fn iter(&self) -> Iter<T> {
|
|
|
Iter {
|
|
|
front: self.front,
|
|
|
back: self.back,
|
|
|
len: self.len,
|
|
|
_boo: PhantomData,
|
|
|
}
|
|
|
}
|
|
|
}
|
|
|
|
|
|
|
|
|
impl<'a, T> IntoIterator for &'a LinkedList<T> {
|
|
|
type IntoIter = Iter<'a, T>;
|
|
|
type Item = &'a T;
|
|
|
|
|
|
fn into_iter(self) -> Self::IntoIter {
|
|
|
self.iter()
|
|
|
}
|
|
|
}
|
|
|
|
|
|
impl<'a, T> Iterator for Iter<'a, T> {
|
|
|
type Item = &'a T;
|
|
|
|
|
|
fn next(&mut self) -> Option<Self::Item> {
|
|
|
// 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 "one-past-the-end" pointers.
|
|
|
if self.len > 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;
|
|
|
&(*node.as_ptr()).elem
|
|
|
})
|
|
|
} else {
|
|
|
None
|
|
|
}
|
|
|
}
|
|
|
|
|
|
fn size_hint(&self) -> (usize, Option<usize>) {
|
|
|
(self.len, Some(self.len))
|
|
|
}
|
|
|
}
|
|
|
|
|
|
impl<'a, T> DoubleEndedIterator for Iter<'a, T> {
|
|
|
fn next_back(&mut self) -> Option<Self::Item> {
|
|
|
if self.len > 0 {
|
|
|
self.back.map(|node| unsafe {
|
|
|
self.len -= 1;
|
|
|
self.back = (*node.as_ptr()).front;
|
|
|
&(*node.as_ptr()).elem
|
|
|
})
|
|
|
} else {
|
|
|
None
|
|
|
}
|
|
|
}
|
|
|
}
|
|
|
|
|
|
impl<'a, T> ExactSizeIterator for Iter<'a, T> {
|
|
|
fn len(&self) -> usize {
|
|
|
self.len
|
|
|
}
|
|
|
}
|
|
|
<span class="boring">}</span></code></pre></pre>
|
|
|
<p>...这只是 <code>.iter()</code>...</p>
|
|
|
<p>我们将在最后粘贴 IterMut，它在很多地方与 <code>mut</code> 的代码完全相同，让我们先敲掉 <code>into_iter</code>。我们仍然可以使用我们屡试不爽的解决方案，即让它包裹我们的集合，并在下一步中使用 <code>pop</code>：</p>
|
|
|
<pre><pre class="playground"><code class="language-rust edition2021"><span class="boring">#![allow(unused)]
|
|
|
</span><span class="boring">fn main() {
|
|
|
</span>pub struct IntoIter<T> {
|
|
|
list: LinkedList<T>,
|
|
|
}
|
|
|
|
|
|
impl<T> LinkedList<T> {
|
|
|
pub fn into_iter(self) -> IntoIter<T> {
|
|
|
IntoIter {
|
|
|
list: self
|
|
|
}
|
|
|
}
|
|
|
}
|
|
|
|
|
|
|
|
|
impl<T> IntoIterator for LinkedList<T> {
|
|
|
type IntoIter = IntoIter<T>;
|
|
|
type Item = T;
|
|
|
|
|
|
fn into_iter(self) -> Self::IntoIter {
|
|
|
self.into_iter()
|
|
|
}
|
|
|
}
|
|
|
|
|
|
impl<T> Iterator for IntoIter<T> {
|
|
|
type Item = T;
|
|
|
|
|
|
fn next(&mut self) -> Option<Self::Item> {
|
|
|
self.list.pop_front()
|
|
|
}
|
|
|
|
|
|
fn size_hint(&self) -> (usize, Option<usize>) {
|
|
|
(self.list.len, Some(self.list.len))
|
|
|
}
|
|
|
}
|
|
|
|
|
|
impl<T> DoubleEndedIterator for IntoIter<T> {
|
|
|
fn next_back(&mut self) -> Option<Self::Item> {
|
|
|
self.list.pop_back()
|
|
|
}
|
|
|
}
|
|
|
|
|
|
impl<T> ExactSizeIterator for IntoIter<T> {
|
|
|
fn len(&self) -> usize {
|
|
|
self.list.len
|
|
|
}
|
|
|
}
|
|
|
<span class="boring">}</span></code></pre></pre>
|
|
|
<p>仍然是一大堆模板，但至少是令人满意的模板。</p>
|
|
|
<p>好了，这是我们所有的代码，其中包含了所有的组合：</p>
|
|
|
<pre><pre class="playground"><code class="language-rust edition2021"><span class="boring">#![allow(unused)]
|
|
|
</span><span class="boring">fn main() {
|
|
|
</span>use std::ptr::NonNull;
|
|
|
use std::marker::PhantomData;
|
|
|
|
|
|
pub struct LinkedList<T> {
|
|
|
front: Link<T>,
|
|
|
back: Link<T>,
|
|
|
len: usize,
|
|
|
_boo: PhantomData<T>,
|
|
|
}
|
|
|
|
|
|
type Link<T> = Option<NonNull<Node<T>>>;
|
|
|
|
|
|
struct Node<T> {
|
|
|
front: Link<T>,
|
|
|
back: Link<T>,
|
|
|
elem: T,
|
|
|
}
|
|
|
|
|
|
pub struct Iter<'a, T> {
|
|
|
front: Link<T>,
|
|
|
back: Link<T>,
|
|
|
len: usize,
|
|
|
_boo: PhantomData<&'a T>,
|
|
|
}
|
|
|
|
|
|
pub struct IterMut<'a, T> {
|
|
|
front: Link<T>,
|
|
|
back: Link<T>,
|
|
|
len: usize,
|
|
|
_boo: PhantomData<&'a mut T>,
|
|
|
}
|
|
|
|
|
|
pub struct IntoIter<T> {
|
|
|
list: LinkedList<T>,
|
|
|
}
|
|
|
|
|
|
impl<T> LinkedList<T> {
|
|
|
pub fn new() -> Self {
|
|
|
Self {
|
|
|
front: None,
|
|
|
back: None,
|
|
|
len: 0,
|
|
|
_boo: PhantomData,
|
|
|
}
|
|
|
}
|
|
|
|
|
|
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.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(&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(&mut self) -> Option<T> {
|
|
|
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(&mut self) -> Option<T> {
|
|
|
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(&self) -> Option<&T> {
|
|
|
unsafe {
|
|
|
self.front.map(|node| &(*node.as_ptr()).elem)
|
|
|
}
|
|
|
}
|
|
|
|
|
|
pub fn front_mut(&mut self) -> Option<&mut T> {
|
|
|
unsafe {
|
|
|
self.front.map(|node| &mut (*node.as_ptr()).elem)
|
|
|
}
|
|
|
}
|
|
|
|
|
|
pub fn back(&self) -> Option<&T> {
|
|
|
unsafe {
|
|
|
self.back.map(|node| &(*node.as_ptr()).elem)
|
|
|
}
|
|
|
}
|
|
|
|
|
|
pub fn back_mut(&mut self) -> Option<&mut T> {
|
|
|
unsafe {
|
|
|
self.back.map(|node| &mut (*node.as_ptr()).elem)
|
|
|
}
|
|
|
}
|
|
|
|
|
|
pub fn len(&self) -> usize {
|
|
|
self.len
|
|
|
}
|
|
|
|
|
|
pub fn iter(&self) -> Iter<T> {
|
|
|
Iter {
|
|
|
front: self.front,
|
|
|
back: self.back,
|
|
|
len: self.len,
|
|
|
_boo: PhantomData,
|
|
|
}
|
|
|
}
|
|
|
|
|
|
pub fn iter_mut(&mut self) -> IterMut<T> {
|
|
|
IterMut {
|
|
|
front: self.front,
|
|
|
back: self.back,
|
|
|
len: self.len,
|
|
|
_boo: PhantomData,
|
|
|
}
|
|
|
}
|
|
|
|
|
|
pub fn into_iter(self) -> IntoIter<T> {
|
|
|
IntoIter {
|
|
|
list: self
|
|
|
}
|
|
|
}
|
|
|
}
|
|
|
|
|
|
impl<T> Drop for LinkedList<T> {
|
|
|
fn drop(&mut self) {
|
|
|
// Pop until we have to stop
|
|
|
while let Some(_) = self.pop_front() { }
|
|
|
}
|
|
|
}
|
|
|
|
|
|
impl<'a, T> IntoIterator for &'a LinkedList<T> {
|
|
|
type IntoIter = Iter<'a, T>;
|
|
|
type Item = &'a T;
|
|
|
|
|
|
fn into_iter(self) -> Self::IntoIter {
|
|
|
self.iter()
|
|
|
}
|
|
|
}
|
|
|
|
|
|
impl<'a, T> Iterator for Iter<'a, T> {
|
|
|
type Item = &'a T;
|
|
|
|
|
|
fn next(&mut self) -> Option<Self::Item> {
|
|
|
// 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 "one-past-the-end" pointers.
|
|
|
if self.len > 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;
|
|
|
&(*node.as_ptr()).elem
|
|
|
})
|
|
|
} else {
|
|
|
None
|
|
|
}
|
|
|
}
|
|
|
|
|
|
fn size_hint(&self) -> (usize, Option<usize>) {
|
|
|
(self.len, Some(self.len))
|
|
|
}
|
|
|
}
|
|
|
|
|
|
impl<'a, T> DoubleEndedIterator for Iter<'a, T> {
|
|
|
fn next_back(&mut self) -> Option<Self::Item> {
|
|
|
if self.len > 0 {
|
|
|
self.back.map(|node| unsafe {
|
|
|
self.len -= 1;
|
|
|
self.back = (*node.as_ptr()).front;
|
|
|
&(*node.as_ptr()).elem
|
|
|
})
|
|
|
} else {
|
|
|
None
|
|
|
}
|
|
|
}
|
|
|
}
|
|
|
|
|
|
impl<'a, T> ExactSizeIterator for Iter<'a, T> {
|
|
|
fn len(&self) -> usize {
|
|
|
self.len
|
|
|
}
|
|
|
}
|
|
|
|
|
|
impl<'a, T> IntoIterator for &'a mut LinkedList<T> {
|
|
|
type IntoIter = IterMut<'a, T>;
|
|
|
type Item = &'a mut T;
|
|
|
|
|
|
fn into_iter(self) -> Self::IntoIter {
|
|
|
self.iter_mut()
|
|
|
}
|
|
|
}
|
|
|
|
|
|
impl<'a, T> Iterator for IterMut<'a, T> {
|
|
|
type Item = &'a mut T;
|
|
|
|
|
|
fn next(&mut self) -> Option<Self::Item> {
|
|
|
// 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 "one-past-the-end" pointers.
|
|
|
if self.len > 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;
|
|
|
&mut (*node.as_ptr()).elem
|
|
|
})
|
|
|
} else {
|
|
|
None
|
|
|
}
|
|
|
}
|
|
|
|
|
|
fn size_hint(&self) -> (usize, Option<usize>) {
|
|
|
(self.len, Some(self.len))
|
|
|
}
|
|
|
}
|
|
|
|
|
|
impl<'a, T> DoubleEndedIterator for IterMut<'a, T> {
|
|
|
fn next_back(&mut self) -> Option<Self::Item> {
|
|
|
if self.len > 0 {
|
|
|
self.back.map(|node| unsafe {
|
|
|
self.len -= 1;
|
|
|
self.back = (*node.as_ptr()).front;
|
|
|
&mut (*node.as_ptr()).elem
|
|
|
})
|
|
|
} else {
|
|
|
None
|
|
|
}
|
|
|
}
|
|
|
}
|
|
|
|
|
|
impl<'a, T> ExactSizeIterator for IterMut<'a, T> {
|
|
|
fn len(&self) -> usize {
|
|
|
self.len
|
|
|
}
|
|
|
}
|
|
|
|
|
|
impl<T> IntoIterator for LinkedList<T> {
|
|
|
type IntoIter = IntoIter<T>;
|
|
|
type Item = T;
|
|
|
|
|
|
fn into_iter(self) -> Self::IntoIter {
|
|
|
self.into_iter()
|
|
|
}
|
|
|
}
|
|
|
|
|
|
impl<T> Iterator for IntoIter<T> {
|
|
|
type Item = T;
|
|
|
|
|
|
fn next(&mut self) -> Option<Self::Item> {
|
|
|
self.list.pop_front()
|
|
|
}
|
|
|
|
|
|
fn size_hint(&self) -> (usize, Option<usize>) {
|
|
|
(self.list.len, Some(self.list.len))
|
|
|
}
|
|
|
}
|
|
|
|
|
|
impl<T> DoubleEndedIterator for IntoIter<T> {
|
|
|
fn next_back(&mut self) -> Option<Self::Item> {
|
|
|
self.list.pop_back()
|
|
|
}
|
|
|
}
|
|
|
|
|
|
impl<T> ExactSizeIterator for IntoIter<T> {
|
|
|
fn len(&self) -> 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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