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use core::fmt;
use core::future::Future;
use core::marker::PhantomData;
use core::ops::{Deref, DerefMut};
use core::pin::Pin;
use core::ptr::NonNull;
use core::task::{Context, Poll};
use super::RawAccessGuard;
/// Guard for data exclusively borrowed from a slot in the virtual machine.
///
/// These guards are necessary, since we need to guarantee certain forms of
/// access depending on what we do. Releasing the guard releases the access.
pub struct BorrowMut<'a, T: ?Sized> {
data: NonNull<T>,
guard: Option<RawAccessGuard>,
_marker: PhantomData<&'a mut T>,
}
impl<'a, T: ?Sized> BorrowMut<'a, T> {
/// Construct a borrow mut from static data.
#[inline]
pub(crate) fn from_ref(data: &'a mut T) -> Self {
Self {
data: NonNull::from(data),
guard: None,
_marker: PhantomData,
}
}
/// Construct a new exclusive guard.
///
/// # Safety
///
/// since this has implications for releasing access, the caller must
/// ensure that access has been acquired correctly using e.g.
/// [Access::exclusive]. Otherwise access can be release incorrectly once
/// this guard is dropped.
#[inline]
pub(crate) unsafe fn new(data: NonNull<T>, guard: RawAccessGuard) -> Self {
Self {
data,
guard: Some(guard),
_marker: PhantomData,
}
}
/// Map the mutable reference.
///
/// # Examples
///
/// ```
/// use rune::runtime::{BorrowMut, Bytes};
/// use rune::alloc::try_vec;
///
/// let bytes = rune::to_value(Bytes::from_vec(try_vec![1, 2, 3, 4]))?;
/// let bytes = bytes.borrow_mut::<Bytes>()?;
///
/// let mut bytes = BorrowMut::map(bytes, |bytes| &mut bytes[0..2]);
///
/// assert_eq!(&mut bytes[..], &mut [1u8, 2u8][..]);
/// # Ok::<_, rune::support::Error>(())
/// ```
#[inline]
pub fn map<U: ?Sized>(mut this: Self, m: impl FnOnce(&mut T) -> &mut U) -> BorrowMut<'a, U> {
// SAFETY: This is safe per construction.
unsafe {
BorrowMut {
data: NonNull::from(m(this.data.as_mut())),
guard: this.guard,
_marker: PhantomData,
}
}
}
/// Try to map the mutable reference to a projection.
///
/// # Examples
///
/// ```
/// use rune::runtime::{BorrowMut, Bytes};
/// use rune::alloc::try_vec;
///
/// let bytes = rune::to_value(Bytes::from_vec(try_vec![1, 2, 3, 4]))?;
/// let bytes = bytes.borrow_mut::<Bytes>()?;
///
/// let Ok(mut bytes) = BorrowMut::try_map(bytes, |bytes| bytes.get_mut(0..2)) else {
/// panic!("Conversion failed");
/// };
///
/// assert_eq!(&mut bytes[..], &mut [1u8, 2u8][..]);
/// # Ok::<_, rune::support::Error>(())
/// ```
#[inline]
pub fn try_map<U: ?Sized>(
mut this: Self,
m: impl FnOnce(&mut T) -> Option<&mut U>,
) -> Result<BorrowMut<'a, U>, Self> {
unsafe {
let Some(data) = m(this.data.as_mut()) else {
return Err(BorrowMut {
data: this.data,
guard: this.guard,
_marker: PhantomData,
});
};
Ok(BorrowMut {
data: NonNull::from(data),
guard: this.guard,
_marker: PhantomData,
})
}
}
}
impl<T: ?Sized> Deref for BorrowMut<'_, T> {
type Target = T;
fn deref(&self) -> &Self::Target {
// SAFETY: This is correct per construction.
unsafe { self.data.as_ref() }
}
}
impl<T: ?Sized> DerefMut for BorrowMut<'_, T> {
fn deref_mut(&mut self) -> &mut Self::Target {
// SAFETY: This is correct per construction.
unsafe { self.data.as_mut() }
}
}
impl<T: ?Sized> fmt::Debug for BorrowMut<'_, T>
where
T: fmt::Debug,
{
fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
fmt::Debug::fmt(&**self, fmt)
}
}
impl<F> Future for BorrowMut<'_, F>
where
F: Unpin + Future,
{
type Output = F::Output;
fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
// NB: inner Future is Unpin.
let this = self.get_mut();
Pin::new(&mut **this).poll(cx)
}
}