Line data Source code
1 : use std::ops::{Deref, DerefMut};
2 :
3 : /// A generic trait which exposes types of cache's key and value,
4 : /// as well as the notion of cache entry invalidation.
5 : /// This is useful for [`Cached`].
6 : pub trait Cache {
7 : /// Entry's key.
8 : type Key;
9 :
10 : /// Entry's value.
11 : type Value;
12 :
13 : /// Used for entry invalidation.
14 : type LookupInfo<Key>;
15 :
16 : /// Invalidate an entry using a lookup info.
17 : /// We don't have an empty default impl because it's error-prone.
18 : fn invalidate(&self, _: &Self::LookupInfo<Self::Key>);
19 : }
20 :
21 : impl<C: Cache> Cache for &C {
22 : type Key = C::Key;
23 : type Value = C::Value;
24 : type LookupInfo<Key> = C::LookupInfo<Key>;
25 :
26 8 : fn invalidate(&self, info: &Self::LookupInfo<Self::Key>) {
27 8 : C::invalidate(self, info)
28 8 : }
29 : }
30 :
31 : /// Wrapper for convenient entry invalidation.
32 : pub struct Cached<C: Cache, V = <C as Cache>::Value> {
33 : /// Cache + lookup info.
34 : pub token: Option<(C, C::LookupInfo<C::Key>)>,
35 :
36 : /// The value itself.
37 : pub value: V,
38 : }
39 :
40 : impl<C: Cache, V> Cached<C, V> {
41 : /// Place any entry into this wrapper; invalidation will be a no-op.
42 24 : pub fn new_uncached(value: V) -> Self {
43 24 : Self { token: None, value }
44 24 : }
45 :
46 6 : pub fn take_value(self) -> (Cached<C, ()>, V) {
47 6 : (
48 6 : Cached {
49 6 : token: self.token,
50 6 : value: (),
51 6 : },
52 6 : self.value,
53 6 : )
54 6 : }
55 :
56 : /// Drop this entry from a cache if it's still there.
57 10 : pub fn invalidate(self) -> V {
58 10 : if let Some((cache, info)) = &self.token {
59 8 : cache.invalidate(info);
60 8 : }
61 10 : self.value
62 10 : }
63 :
64 : /// Tell if this entry is actually cached.
65 36 : pub fn cached(&self) -> bool {
66 36 : self.token.is_some()
67 36 : }
68 : }
69 :
70 : impl<C: Cache, V> Deref for Cached<C, V> {
71 : type Target = V;
72 :
73 6 : fn deref(&self) -> &Self::Target {
74 6 : &self.value
75 6 : }
76 : }
77 :
78 : impl<C: Cache, V> DerefMut for Cached<C, V> {
79 52 : fn deref_mut(&mut self) -> &mut Self::Target {
80 52 : &mut self.value
81 52 : }
82 : }
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