style/rule_tree/
unsafe_box.rs

1/* This Source Code Form is subject to the terms of the Mozilla Public
2 * License, v. 2.0. If a copy of the MPL was not distributed with this
3 * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
4
5#![allow(unsafe_code)]
6
7use std::mem::ManuallyDrop;
8use std::ops::Deref;
9use std::ptr;
10
11/// An unsafe box, derefs to `T`.
12pub(super) struct UnsafeBox<T> {
13    inner: ManuallyDrop<Box<T>>,
14}
15
16impl<T> UnsafeBox<T> {
17    /// Creates a new unsafe box.
18    pub(super) fn from_box(value: Box<T>) -> Self {
19        Self {
20            inner: ManuallyDrop::new(value),
21        }
22    }
23
24    /// Creates a new box from a pointer.
25    ///
26    /// # Safety
27    ///
28    /// The input should point to a valid `T`.
29    pub(super) unsafe fn from_raw(ptr: *mut T) -> Self {
30        Self {
31            inner: ManuallyDrop::new(Box::from_raw(ptr)),
32        }
33    }
34
35    /// Creates a new unsafe box from an existing one.
36    ///
37    /// # Safety
38    ///
39    /// There is no refcounting or whatever else in an unsafe box, so this
40    /// operation can lead to double frees.
41    pub(super) unsafe fn clone(this: &Self) -> Self {
42        Self {
43            inner: ptr::read(&this.inner),
44        }
45    }
46
47    /// Returns a mutable reference to the inner value of this unsafe box.
48    ///
49    /// # Safety
50    ///
51    /// Given `Self::clone`, nothing prevents anyone from creating
52    /// multiple mutable references to the inner value, which is completely UB.
53    pub(crate) unsafe fn deref_mut(this: &mut Self) -> &mut T {
54        &mut this.inner
55    }
56
57    /// Drops the inner value of this unsafe box.
58    ///
59    /// # Safety
60    ///
61    /// Given this doesn't consume the unsafe box itself, this has the same
62    /// safety caveats as `ManuallyDrop::drop`.
63    pub(super) unsafe fn drop(this: &mut Self) {
64        ManuallyDrop::drop(&mut this.inner)
65    }
66}
67
68impl<T> Deref for UnsafeBox<T> {
69    type Target = T;
70
71    fn deref(&self) -> &Self::Target {
72        &self.inner
73    }
74}
style/rule_tree/unsafe_box.rs

style/rule_tree/
unsafe_box.rs
