src/librustc_data_structures/veccell/mod.rs

   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> {
  15     data: UnsafeCell<Vec<T>>,
  16 }
  17
  18 impl<T> VecCell<T> {
  19     pub fn with_capacity(capacity: usize) -> VecCell<T> {
  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 }