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1 | // Copyright 2012-2014 The Rust Project Developers. See the COPYRIGHT |
2 | // file at the top-level directory of this distribution and at | |
3 | // http://rust-lang.org/COPYRIGHT. | |
4 | // | |
5 | // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or | |
6 | // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license | |
7 | // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your | |
8 | // option. This file may not be copied, modified, or distributed | |
9 | // except according to those terms. | |
10 | ||
11 | use std::cell::UnsafeCell; | |
12 | use std::mem; | |
13 | ||
14 | pub struct VecCell<T> { | |
54a0048b | 15 | data: UnsafeCell<Vec<T>>, |
9cc50fc6 SL |
16 | } |
17 | ||
18 | impl<T> VecCell<T> { | |
54a0048b | 19 | pub fn with_capacity(capacity: usize) -> VecCell<T> { |
9cc50fc6 SL |
20 | VecCell { data: UnsafeCell::new(Vec::with_capacity(capacity)) } |
21 | } | |
22 | ||
23 | #[inline] | |
24 | pub fn push(&self, data: T) -> usize { | |
25 | // The logic here, and in `swap` below, is that the `push` | |
26 | // method on the vector will not recursively access this | |
27 | // `VecCell`. Therefore, we can temporarily obtain mutable | |
28 | // access, secure in the knowledge that even if aliases exist | |
29 | // -- indeed, even if aliases are reachable from within the | |
30 | // vector -- they will not be used for the duration of this | |
31 | // particular fn call. (Note that we also are relying on the | |
32 | // fact that `VecCell` is not `Sync`.) | |
33 | unsafe { | |
34 | let v = self.data.get(); | |
35 | (*v).push(data); | |
36 | (*v).len() | |
37 | } | |
38 | } | |
39 | ||
40 | pub fn swap(&self, mut data: Vec<T>) -> Vec<T> { | |
41 | unsafe { | |
42 | let v = self.data.get(); | |
43 | mem::swap(&mut *v, &mut data); | |
44 | } | |
45 | data | |
46 | } | |
47 | } |