edn/
intern_set.rs

1// Copyright 2016 Mozilla
2//
3// Licensed under the Apache License, Version 2.0 (the "License"); you may not use
4// this file except in compliance with the License. You may obtain a copy of the
5// License at http://www.apache.org/licenses/LICENSE-2.0
6// Unless required by applicable law or agreed to in writing, software distributed
7// under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR
8// CONDITIONS OF ANY KIND, either express or implied. See the License for the
9// specific language governing permissions and limitations under the License.
10
11use std::collections::HashSet;
12use std::hash::Hash;
13use std::ops::{Deref, DerefMut};
14
15use crate::ValueRc;
16
17/// An `InternSet` allows to "intern" some potentially large values, maintaining a single value
18/// instance owned by the `InternSet` and leaving consumers with lightweight ref-counted handles to
19/// the large owned value.  This can avoid expensive clone() operations.
20///
21/// In Mentat, such large values might be strings or arbitrary [a v] pairs.
22///
23/// See https://en.wikipedia.org/wiki/String_interning for discussion.
24#[derive(Clone, Debug, Default, Eq, PartialEq)]
25pub struct InternSet<T>
26where
27    T: Eq + Hash,
28{
29    inner: HashSet<ValueRc<T>>,
30}
31
32impl<T> Deref for InternSet<T>
33where
34    T: Eq + Hash,
35{
36    type Target = HashSet<ValueRc<T>>;
37
38    fn deref(&self) -> &Self::Target {
39        &self.inner
40    }
41}
42
43impl<T> DerefMut for InternSet<T>
44where
45    T: Eq + Hash,
46{
47    fn deref_mut(&mut self) -> &mut Self::Target {
48        &mut self.inner
49    }
50}
51
52impl<T> InternSet<T>
53where
54    T: Eq + Hash,
55{
56    pub fn new() -> InternSet<T> {
57        InternSet {
58            inner: HashSet::new(),
59        }
60    }
61
62    /// Intern a value, providing a ref-counted handle to the interned value.
63    ///
64    /// ```
65    /// use edn::{InternSet, ValueRc};
66    ///
67    /// let mut s = InternSet::new();
68    ///
69    /// let one = "foo".to_string();
70    /// let two = ValueRc::new("foo".to_string());
71    ///
72    /// let out_one = s.intern(one);
73    /// assert_eq!(out_one, two);
74    /// // assert!(!&out_one.ptr_eq(&two));      // Nightly-only.
75    ///
76    /// let out_two = s.intern(two);
77    /// assert_eq!(out_one, out_two);
78    /// assert_eq!(1, s.len());
79    /// // assert!(&out_one.ptr_eq(&out_two));   // Nightly-only.
80    /// ```
81    pub fn intern<R: Into<ValueRc<T>>>(&mut self, value: R) -> ValueRc<T> {
82        let key: ValueRc<T> = value.into();
83        if self.inner.insert(key.clone()) {
84            key
85        } else {
86            self.inner.get(&key).unwrap().clone()
87        }
88    }
89}
edn/intern_set.rs

edn/
intern_set.rs
