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        unsafe {
31            Self {
32                inner: ManuallyDrop::new(Box::from_raw(ptr)),
33            }
34        }
35    }
36
37    /// Creates a new unsafe box from an existing one.
38    ///
39    /// # Safety
40    ///
41    /// There is no refcounting or whatever else in an unsafe box, so this
42    /// operation can lead to double frees.
43    pub(super) unsafe fn clone(this: &Self) -> Self {
44        unsafe {
45            Self {
46                inner: ptr::read(&this.inner),
47            }
48        }
49    }
50
51    /// Returns a mutable reference to the inner value of this unsafe box.
52    ///
53    /// # Safety
54    ///
55    /// Given `Self::clone`, nothing prevents anyone from creating
56    /// multiple mutable references to the inner value, which is completely UB.
57    pub(crate) unsafe fn deref_mut(this: &mut Self) -> &mut T {
58        &mut this.inner
59    }
60
61    /// Drops the inner value of this unsafe box.
62    ///
63    /// # Safety
64    ///
65    /// Given this doesn't consume the unsafe box itself, this has the same
66    /// safety caveats as `ManuallyDrop::drop`.
67    pub(super) unsafe fn drop(this: &mut Self) {
68        unsafe { ManuallyDrop::drop(&mut this.inner) }
69    }
70}
71
72impl<T> Deref for UnsafeBox<T> {
73    type Target = T;
74
75    fn deref(&self) -> &Self::Target {
76        &self.inner
77    }
78}
style/rule_tree/unsafe_box.rs

style/rule_tree/
unsafe_box.rs
