/* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at
https://mozilla.org/MPL/2.0/. */
#![allow(unsafe_code)]
use std::mem::ManuallyDrop;
use std::ops::Deref;
use std::ptr;
/// An unsafe box, derefs to `T`.
pub(super) struct UnsafeBox<T> {
inner: ManuallyDrop<Box<T>>,
}
impl<T> UnsafeBox<T> {
/// Creates a new unsafe box.
pub(super) fn from_box(value: Box<T>) -> Self {
Self {
inner: ManuallyDrop::new(value),
}
}
/// Creates a new box from a pointer.
///
/// # Safety
///
/// The input should point to a valid `T`.
pub(super) unsafe fn from_raw(ptr: *mut T) -> Self {
Self {
inner: ManuallyDrop::new(Box::from_raw(ptr)),
}
}
/// Creates a new unsafe box from an existing one.
///
/// # Safety
///
/// There is no refcounting or whatever else in an unsafe box, so this
/// operation can lead to double frees.
pub(super) unsafe fn clone(this: &Self) -> Self {
Self {
inner: ptr::read(&this.inner),
}
}
/// Returns a mutable reference to the inner value of this unsafe box.
///
/// # Safety
///
/// Given `Self::clone`, nothing prevents anyone from creating
/// multiple mutable references to the inner value, which is completely UB.
pub(crate) unsafe fn deref_mut(this: &mut Self) -> &mut T {
&mut this.inner
}
/// Drops the inner value of this unsafe box.
///
/// # Safety
///
/// Given this doesn't consume the unsafe box itself, this has the same
/// safety caveats as `ManuallyDrop::drop`.
pub(super) unsafe fn drop(this: &mut Self) {
ManuallyDrop::drop(&mut this.inner)
}
}
impl<T> Deref for UnsafeBox<T> {
type Target = T;
fn deref(&self) -> &Self::Target {
&self.inner
}
}
