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