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Add MappedAtomicRef(Mut) #15

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Add MappedAtomicRef(Mut) #15

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101 changes: 101 additions & 0 deletions src/lib.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -416,6 +416,18 @@ impl<'b, T: ?Sized> AtomicRef<'b, T> {
borrow: orig.borrow,
})
}

/// Make a new `MappedAtomicRef` using the borrowed data.
#[inline]
pub fn map_into<U, F>(orig: AtomicRef<'b, T>, f: F) -> MappedAtomicRef<'b, U>
where
F: FnOnce(&'b T) -> U,
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'b is the lifetime of the shared borrow of the AtomicRefCell (and not actually the lifetime that &T is valid for which is up until the AtomicRef/MappedAtomicRef is dropped).

Unfortunately, as noted here rust-lang/rust#70263 (comment), that means this API allows for UB.

E.g. the following test compiles:

#[test]
fn owned_map() {
    use atomic_refcell::*;

    let cell = AtomicRefCell::new(3u8);
    let mut other = &mut 0u8;

    let guard = AtomicRefMut::map_into(cell.borrow_mut(), |inner: &mut u8| {
        // sneak reference out
        other = inner;
    });
    // guard dropped but reference still accessible via `other`
    drop(guard);

    assert_eq!(*other, 3);

    *cell.borrow_mut() = 1;

    assert_eq!(*other, 1);
}

There are some potential workarounds noted in the comment I linked, but they can make things difficult to work with.

{
MappedAtomicRef {
value: f(orig.value),
borrow: orig.borrow,
}
}
}

impl<'b, T: ?Sized> AtomicRefMut<'b, T> {
Expand Down Expand Up @@ -443,6 +455,18 @@ impl<'b, T: ?Sized> AtomicRefMut<'b, T> {
borrow: orig.borrow,
})
}

/// Make a new `MappedAtomicRefMut` using the borrowed data.
#[inline]
pub fn map_into<U, F>(orig: AtomicRefMut<'b, T>, f: F) -> MappedAtomicRefMut<'b, U>
where
F: FnOnce(&'b mut T) -> U,
{
MappedAtomicRefMut {
value: f(orig.value),
borrow: orig.borrow,
}
}
}

/// A wrapper type for a mutably borrowed value from an `AtomicRefCell<T>`.
Expand All @@ -467,6 +491,71 @@ impl<'b, T: ?Sized> DerefMut for AtomicRefMut<'b, T> {
}
}

/// A wraper type for data derived from an immutably borrowed value from an `AtomicRefCell`.
pub struct MappedAtomicRef<'b, T> {
value: T,
borrow: AtomicBorrowRef<'b>,
}

impl<'b, T> Deref for MappedAtomicRef<'b, T> {
type Target = T;

#[inline]
fn deref(&self) -> &Self::Target {
&self.value
}
}

impl<'b, T> MappedAtomicRef<'b, T> {
/// Make a new `MappedAtomicRef<T>` using the encapsulated data.
#[inline]
pub fn map_into<U, F>(orig: MappedAtomicRef<'b, T>, f: F) -> MappedAtomicRef<'b, U>
where
F: FnOnce(T) -> U,
{
MappedAtomicRef {
value: f(orig.value),
borrow: orig.borrow,
}
}
}

/// A wraper type for data derived from a mutably borrowed value from an `AtomicRefCell`.
pub struct MappedAtomicRefMut<'b, T> {
value: T,
borrow: AtomicBorrowRefMut<'b>,
}

impl<'b, T> Deref for MappedAtomicRefMut<'b, T> {
type Target = T;

#[inline]
fn deref(&self) -> &Self::Target {
&self.value
}
}

impl<'b, T> DerefMut for MappedAtomicRefMut<'b, T> {
#[inline]
fn deref_mut(&mut self) -> &mut Self::Target {
&mut self.value
}
}

impl<'b, T> MappedAtomicRefMut<'b, T> {
/// Make a new `MappedAtomicRefMut<T>` using the encapsulated data.
#[inline]
pub fn map_into<U, F>(orig: MappedAtomicRefMut<'b, T>, f: F) -> MappedAtomicRefMut<'b, U>
where
F: FnOnce(T) -> U,
{
MappedAtomicRefMut {
value: f(orig.value),
borrow: orig.borrow,
}
}
}

impl<'b, T: ?Sized + Debug + 'b> Debug for AtomicRef<'b, T> {
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
self.value.fmt(f)
Expand All @@ -479,6 +568,18 @@ impl<'b, T: ?Sized + Debug + 'b> Debug for AtomicRefMut<'b, T> {
}
}

impl<'b, T: Debug + 'b> Debug for MappedAtomicRef<'b, T> {
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
self.value.fmt(f)
}
}

impl<'b, T: Debug + 'b> Debug for MappedAtomicRefMut<'b, T> {
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
self.value.fmt(f)
}
}

impl<T: ?Sized + Debug> Debug for AtomicRefCell<T> {
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
write!(f, "AtomicRefCell {{ ... }}")
Expand Down