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// Copyright 2012-2014 The Rust Project Developers. See the COPYRIGHT // file at the top-level directory of this distribution and at // http://rust-lang.org/COPYRIGHT. // // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your // option. This file may not be copied, modified, or distributed // except according to those terms. use std::cell::UnsafeCell; use std::mem; pub struct VecCell<T> { data: UnsafeCell<Vec<T>>, } impl<T> VecCell<T> { pub fn with_capacity(capacity: usize) -> VecCell<T> { VecCell { data: UnsafeCell::new(Vec::with_capacity(capacity)) } } #[inline] pub fn push(&self, data: T) -> usize { // The logic here, and in `swap` below, is that the `push` // method on the vector will not recursively access this // `VecCell`. Therefore, we can temporarily obtain mutable // access, secure in the knowledge that even if aliases exist // -- indeed, even if aliases are reachable from within the // vector -- they will not be used for the duration of this // particular fn call. (Note that we also are relying on the // fact that `VecCell` is not `Sync`.) unsafe { let v = self.data.get(); (*v).push(data); (*v).len() } } pub fn swap(&self, mut data: Vec<T>) -> Vec<T> { unsafe { let v = self.data.get(); mem::swap(&mut *v, &mut data); } data } }