1use std::{collections, hash, ops::DerefMut, sync};
2
3/// Trait implemented by types which can be cleared in place, retaining any
4/// allocated memory.
5///
6/// This is essentially a generalization of methods on standard library
7/// collection types, including as [`Vec::clear`], [`String::clear`], and
8/// [`HashMap::clear`]. These methods drop all data stored in the collection,
9/// but retain the collection's heap allocation for future use. Types such as
10/// `BTreeMap`, whose `clear` methods drops allocations, should not
11/// implement this trait.
12///
13/// When implemented for types which do not own a heap allocation, `Clear`
14/// should reset the type in place if possible. If the type has an empty state
15/// or stores `Option`s, those values should be reset to the empty state. For
16/// "plain old data" types, which hold no pointers to other data and do not have
17/// an empty or initial state, it's okay for a `Clear` implementation to be a
18/// no-op. In that case, it essentially serves as a marker indicating that the
19/// type may be reused to store new data.
20///
21/// [`Vec::clear`]: https://doc.rust-lang.org/stable/std/vec/struct.Vec.html#method.clear
22/// [`String::clear`]: https://doc.rust-lang.org/stable/std/string/struct.String.html#method.clear
23/// [`HashMap::clear`]: https://doc.rust-lang.org/stable/std/collections/struct.HashMap.html#method.clear
24pub trait Clear {
25 /// Clear all data in `self`, retaining the allocated capacithy.
26 fn clear(&mut self);
27}
28
29impl<T> Clear for Option<T> {
30 fn clear(&mut self) {
31 let _ = self.take();
32 }
33}
34
35impl<T> Clear for Box<T>
36where
37 T: Clear,
38{
39 #[inline]
40 fn clear(&mut self) {
41 self.deref_mut().clear()
42 }
43}
44
45impl<T> Clear for Vec<T> {
46 #[inline]
47 fn clear(&mut self) {
48 Vec::clear(self)
49 }
50}
51
52impl<K, V, S> Clear for collections::HashMap<K, V, S>
53where
54 K: hash::Hash + Eq,
55 S: hash::BuildHasher,
56{
57 #[inline]
58 fn clear(&mut self) {
59 collections::HashMap::clear(self)
60 }
61}
62
63impl<T, S> Clear for collections::HashSet<T, S>
64where
65 T: hash::Hash + Eq,
66 S: hash::BuildHasher,
67{
68 #[inline]
69 fn clear(&mut self) {
70 collections::HashSet::clear(self)
71 }
72}
73
74impl Clear for String {
75 #[inline]
76 fn clear(&mut self) {
77 String::clear(self)
78 }
79}
80
81impl<T: Clear> Clear for sync::Mutex<T> {
82 #[inline]
83 fn clear(&mut self) {
84 self.get_mut().unwrap().clear();
85 }
86}
87
88impl<T: Clear> Clear for sync::RwLock<T> {
89 #[inline]
90 fn clear(&mut self) {
91 self.write().unwrap().clear();
92 }
93}
94
95#[cfg(all(loom, test))]
96impl<T: Clear> Clear for crate::sync::alloc::Track<T> {
97 fn clear(&mut self) {
98 self.get_mut().clear()
99 }
100}
101