46 lines
1.6 KiB
Rust
46 lines
1.6 KiB
Rust
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// Copyright 2016 Mozilla
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//
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// Licensed under the Apache License, Version 2.0 (the "License"); you may not use
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// this file except in compliance with the License. You may obtain a copy of the
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// License at http://www.apache.org/licenses/LICENSE-2.0
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// Unless required by applicable law or agreed to in writing, software distributed
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// under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR
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// CONDITIONS OF ANY KIND, either express or implied. See the License for the
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// specific language governing permissions and limitations under the License.
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#![allow(dead_code)]
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use std::collections::HashSet;
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use std::hash::Hash;
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use std::rc::Rc;
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/// An `InternSet` allows to "intern" some potentially large values, maintaining a single value
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/// instance owned by the `InternSet` and leaving consumers with lightweight ref-counted handles to
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/// the large owned value. This can avoid expensive clone() operations.
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///
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/// In Mentat, such large values might be strings or arbitrary [a v] pairs.
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///
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/// See https://en.wikipedia.org/wiki/String_interning for discussion.
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#[derive(Clone, Debug, Default, Eq, PartialEq)]
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pub struct InternSet<T> where T: Eq + Hash {
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pub inner: HashSet<Rc<T>>,
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}
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impl<T> InternSet<T> where T: Eq + Hash {
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pub fn new() -> InternSet<T> {
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InternSet {
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inner: HashSet::new(),
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}
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}
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/// Intern a value, providing a ref-counted handle to the interned value.
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pub fn intern(&mut self, value: T) -> Rc<T> {
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let key = Rc::new(value);
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if self.inner.insert(key.clone()) {
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key
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} else {
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self.inner.get(&key).unwrap().clone()
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}
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}
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}
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