1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
|
/* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at https://mozilla.org/MPL/2.0/. */
//! A persistent, thread-safe singly-linked list.
use std::sync::Arc;
pub struct PersistentList<T> {
head: PersistentListLink<T>,
length: usize,
}
struct PersistentListEntry<T> {
value: T,
next: PersistentListLink<T>,
}
type PersistentListLink<T> = Option<Arc<PersistentListEntry<T>>>;
impl<T> PersistentList<T>
where
T: Send + Sync,
{
#[inline]
pub fn new() -> PersistentList<T> {
PersistentList {
head: None,
length: 0,
}
}
#[inline]
pub fn len(&self) -> usize {
self.length
}
#[inline]
pub fn front(&self) -> Option<&T> {
self.head.as_ref().map(|head| &head.value)
}
#[inline]
pub fn prepend_elem(&self, value: T) -> PersistentList<T> {
PersistentList {
head: Some(Arc::new(PersistentListEntry {
value,
next: self.head.clone(),
})),
length: self.length + 1,
}
}
#[inline]
pub fn iter(&self) -> PersistentListIterator<T> {
// This could clone (and would not need the lifetime if it did), but then it would incur
// atomic operations on every call to `.next()`. Bad.
PersistentListIterator {
entry: self.head.as_deref(),
}
}
}
impl<T> Clone for PersistentList<T>
where
T: Send + Sync,
{
fn clone(&self) -> PersistentList<T> {
// This establishes the persistent nature of this list: we can clone a list by just cloning
// its head.
PersistentList {
head: self.head.clone(),
length: self.length,
}
}
}
pub struct PersistentListIterator<'a, T>
where
T: Send + Sync,
{
entry: Option<&'a PersistentListEntry<T>>,
}
impl<'a, T> Iterator for PersistentListIterator<'a, T>
where
T: Send + Sync + 'static,
{
type Item = &'a T;
#[inline]
fn next(&mut self) -> Option<&'a T> {
let entry = self.entry?;
let value = &entry.value;
self.entry = match entry.next {
None => None,
Some(ref entry) => Some(&**entry),
};
Some(value)
}
}
|
