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
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
use std::ops::{Index, IndexMut};
#[derive(Clone, Copy, Debug, PartialEq, Eq, Hash)]
pub struct NodeId(pub usize);
#[derive(Debug)]
pub enum Arena<'a, T: 'a> {
Owned(Vec<Option<T>>),
Borrowed(&'a mut Vec<Option<T>>)
}
impl<'a, T> Default for Arena<'a, T> {
fn default() -> Self {
Arena::Owned(Vec::new())
}
}
impl<'a, T> Arena<'a, T> {
pub fn new() -> Self {
Self::default()
}
pub fn with_arena(arena: &'a mut Vec<Option<T>>) -> Self {
Arena::Borrowed(arena)
}
pub fn reference<'b>(&'b mut self) -> Arena<'b, T> {
Arena::with_arena(self.get_mut())
}
pub fn into_inner(self) -> Vec<Option<T>> {
match self {
Arena::Owned(inner) => inner,
Arena::Borrowed(_) => panic!("can't move out of borrowed arena")
}
}
pub fn get_ref(&self) -> &[Option<T>] {
match self {
Arena::Owned(inner) => inner,
Arena::Borrowed(inner) => inner
}
}
fn get_mut(&mut self) -> &mut Vec<Option<T>> {
match self {
Arena::Owned(inner) => inner,
Arena::Borrowed(inner) => inner
}
}
pub fn iter(&self) -> ArenaIter<T> {
self.into_iter()
}
pub fn insert(&mut self, elem: T) -> NodeId {
let inner = self.get_mut();
inner.push(Some(elem));
NodeId(inner.len() - 1)
}
pub fn take(&mut self, index: NodeId) -> T {
self.get_mut()[index.0].take().expect("this index has been taken")
}
pub fn ids(&'a self) -> impl Iterator<Item = NodeId> + 'a {
let inner = self.get_ref();
inner
.iter()
.enumerate()
.filter(|(_, val)| val.is_some())
.map(|(id, _)| NodeId(id))
}
}
impl<'a, T> Index<NodeId> for Arena<'a, T> {
type Output = T;
fn index(&self, index: NodeId) -> &Self::Output {
&self.get_ref()[index.0].as_ref().expect("this index has been taken")
}
}
impl<'a, T> IndexMut<NodeId> for Arena<'a, T> {
fn index_mut(&mut self, index: NodeId) -> &mut Self::Output {
self.get_mut()[index.0].as_mut().expect("this index has been taken")
}
}
impl<'r, 'a, T> IntoIterator for &'r Arena<'a, T> {
type Item = &'r T;
type IntoIter = ArenaIter<'r, T>;
fn into_iter(self) -> Self::IntoIter {
ArenaIter {
slice: self.get_ref(),
index: 0
}
}
}
impl<'a, T> Clone for Arena<'a, T> where T: Clone {
fn clone(&self) -> Self {
match self {
Arena::Owned(inner) => Arena::Owned(inner.to_vec()),
Arena::Borrowed(inner) => Arena::Owned(inner.to_vec())
}
}
}
pub struct ArenaIter<'a, T: 'a> {
slice: &'a [Option<T>],
index: usize
}
impl<'a, T> Iterator for ArenaIter<'a, T> {
type Item = &'a T;
fn next(&mut self) -> Option<Self::Item> {
while let Some(None) = self.slice.get(self.index) {
self.index += 1;
}
let item = self.slice.get(self.index).map(|item| item.as_ref().unwrap());
self.index += 1;
item
}
}
#[cfg(test)]
mod tests {
use super::{Arena, NodeId};
#[test]
fn it_should_return_node_ids() {
let mut arena: Arena<'static, u32> = Arena::new();
arena.insert(100);
arena.insert(101);
let ids: Vec<NodeId> = arena.ids().collect();
assert_eq!(
ids,
vec![NodeId(0), NodeId(1)]
)
}
#[test]
fn it_should_not_return_node_ids_of_removed_elements() {
let mut arena: Arena<'static, u32> = Arena::new();
arena.insert(100);
arena.insert(101);
arena.take(NodeId(0));
let ids: Vec<NodeId> = arena.ids().collect();
assert_eq!(
ids,
vec![NodeId(1)]
)
}
}