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use rustc_index::vec::{Idx, IndexVec};
use std::{mem, rc::Rc, sync::Arc};
pub trait IdFunctor: Sized {
type Inner;
fn try_map_id<F, E>(self, f: F) -> Result<Self, E>
where
F: FnMut(Self::Inner) -> Result<Self::Inner, E>;
}
impl<T> IdFunctor for Box<T> {
type Inner = T;
#[inline]
fn try_map_id<F, E>(self, mut f: F) -> Result<Self, E>
where
F: FnMut(Self::Inner) -> Result<Self::Inner, E>,
{
let raw = Box::into_raw(self);
Ok(unsafe {
// SAFETY: The raw pointer points to a valid value of type `T`.
let value = raw.read();
// SAFETY: Converts `Box<T>` to `Box<MaybeUninit<T>>` which is the
// inverse of `Box::assume_init()` and should be safe.
let raw: Box<mem::MaybeUninit<T>> = Box::from_raw(raw.cast());
// SAFETY: Write the mapped value back into the `Box`.
Box::write(raw, f(value)?)
})
}
}
impl<T> IdFunctor for Vec<T> {
type Inner = T;
#[inline]
fn try_map_id<F, E>(self, f: F) -> Result<Self, E>
where
F: FnMut(Self::Inner) -> Result<Self::Inner, E>,
{
self.into_iter().map(f).collect()
}
}
impl<T> IdFunctor for Box<[T]> {
type Inner = T;
#[inline]
fn try_map_id<F, E>(self, f: F) -> Result<Self, E>
where
F: FnMut(Self::Inner) -> Result<Self::Inner, E>,
{
Vec::from(self).try_map_id(f).map(Into::into)
}
}
impl<I: Idx, T> IdFunctor for IndexVec<I, T> {
type Inner = T;
#[inline]
fn try_map_id<F, E>(self, f: F) -> Result<Self, E>
where
F: FnMut(Self::Inner) -> Result<Self::Inner, E>,
{
self.raw.try_map_id(f).map(IndexVec::from_raw)
}
}
macro_rules! rc {
($($rc:ident),+) => {$(
impl<T: Clone> IdFunctor for $rc<T> {
type Inner = T;
#[inline]
fn try_map_id<F, E>(mut self, mut f: F) -> Result<Self, E>
where
F: FnMut(Self::Inner) -> Result<Self::Inner, E>,
{
// We merely want to replace the contained `T`, if at all possible,
// so that we don't needlessly allocate a new `$rc` or indeed clone
// the contained type.
unsafe {
// First step is to ensure that we have a unique reference to
// the contained type, which `$rc::make_mut` will accomplish (by
// allocating a new `$rc` and cloning the `T` only if required).
// This is done *before* casting to `$rc<ManuallyDrop<T>>` so that
// panicking during `make_mut` does not leak the `T`.
$rc::make_mut(&mut self);
// Casting to `$rc<ManuallyDrop<T>>` is safe because `ManuallyDrop`
// is `repr(transparent)`.
let ptr = $rc::into_raw(self).cast::<mem::ManuallyDrop<T>>();
let mut unique = $rc::from_raw(ptr);
// Call to `$rc::make_mut` above guarantees that `unique` is the
// sole reference to the contained value, so we can avoid doing
// a checked `get_mut` here.
let slot = $rc::get_mut_unchecked(&mut unique);
// Semantically move the contained type out from `unique`, fold
// it, then move the folded value back into `unique`. Should
// folding fail, `ManuallyDrop` ensures that the "moved-out"
// value is not re-dropped.
let owned = mem::ManuallyDrop::take(slot);
let folded = f(owned)?;
*slot = mem::ManuallyDrop::new(folded);
// Cast back to `$rc<T>`.
Ok($rc::from_raw($rc::into_raw(unique).cast()))
}
}
}
)+};
}
rc! { Rc, Arc }
|
