1use std::{
 2    fmt::{self, Debug},
 3    sync::Arc,
 4};
 5
 6#[derive(PartialEq, Eq)]
 7pub enum ArcCow<'a, T: ?Sized> {
 8    Borrowed(&'a T),
 9    Owned(Arc<T>),
10}
11
12use std::hash::{Hash, Hasher};
13
14impl<'a, T: ?Sized + Hash> Hash for ArcCow<'a, T> {
15    fn hash<H: Hasher>(&self, state: &mut H) {
16        match self {
17            Self::Borrowed(borrowed) => Hash::hash(borrowed, state),
18            Self::Owned(owned) => Hash::hash(&**owned, state),
19        }
20    }
21}
22
23impl<'a, T: ?Sized> Clone for ArcCow<'a, T> {
24    fn clone(&self) -> Self {
25        match self {
26            Self::Borrowed(borrowed) => Self::Borrowed(borrowed),
27            Self::Owned(owned) => Self::Owned(owned.clone()),
28        }
29    }
30}
31
32impl<'a, T: ?Sized> From<&'a T> for ArcCow<'a, T> {
33    fn from(s: &'a T) -> Self {
34        Self::Borrowed(s)
35    }
36}
37
38impl<T> From<Arc<T>> for ArcCow<'_, T> {
39    fn from(s: Arc<T>) -> Self {
40        Self::Owned(s)
41    }
42}
43
44impl From<String> for ArcCow<'_, str> {
45    fn from(value: String) -> Self {
46        Self::Owned(value.into())
47    }
48}
49
50impl<'a, T: ?Sized + ToOwned> std::borrow::Borrow<T> for ArcCow<'a, T> {
51    fn borrow(&self) -> &T {
52        match self {
53            ArcCow::Borrowed(borrowed) => borrowed,
54            ArcCow::Owned(owned) => owned.as_ref(),
55        }
56    }
57}
58
59impl<T: ?Sized> std::ops::Deref for ArcCow<'_, T> {
60    type Target = T;
61
62    fn deref(&self) -> &Self::Target {
63        match self {
64            ArcCow::Borrowed(s) => s,
65            ArcCow::Owned(s) => s.as_ref(),
66        }
67    }
68}
69
70impl<T: ?Sized> AsRef<T> for ArcCow<'_, T> {
71    fn as_ref(&self) -> &T {
72        match self {
73            ArcCow::Borrowed(borrowed) => borrowed,
74            ArcCow::Owned(owned) => owned.as_ref(),
75        }
76    }
77}
78
79impl<'a, T: ?Sized + Debug> Debug for ArcCow<'a, T> {
80    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
81        match self {
82            ArcCow::Borrowed(borrowed) => Debug::fmt(borrowed, f),
83            ArcCow::Owned(owned) => Debug::fmt(&**owned, f),
84        }
85    }
86}