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Remove T: Trace bound from GcCellRef<T>; add GcCellRef::clone #118

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merged 2 commits into from
Jan 3, 2021
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Remove T: Trace bound from GcCellRef<T>; add GcCellRef::clone #118

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e548a81
Remove T: Trace bound from GcCellRef<T>
andersk Jan 3, 2021
3df1a9e
Add GcCellRef::clone
andersk Jan 3, 2021
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35 changes: 26 additions & 9 deletions gc/src/lib.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -657,12 +657,29 @@ unsafe impl<T: Trace + ?Sized> Trace for GcCell<T> {
}

/// A wrapper type for an immutably borrowed value from a `GcCell<T>`.
pub struct GcCellRef<'a, T: Trace + ?Sized + 'static> {
pub struct GcCellRef<'a, T: ?Sized + 'static> {
flags: &'a Cell<BorrowFlag>,
value: &'a T,
}

impl<'a, T: Trace + ?Sized> GcCellRef<'a, T> {
impl<'a, T: ?Sized> GcCellRef<'a, T> {
/// Copies a `GcCellRef`.
///
/// The `GcCell` is already immutably borrowed, so this cannot fail.
///
/// This is an associated function that needs to be used as
/// `GcCellRef::clone(...)`. A `Clone` implementation or a method
/// would interfere with the use of `c.borrow().clone()` to clone
/// the contents of a `GcCell`.
#[inline]
pub fn clone(orig: &GcCellRef<'a, T>) -> GcCellRef<'a, T> {
orig.flags.set(orig.flags.get().add_reading());
GcCellRef {
flags: orig.flags,
value: orig.value,
}
}

/// Makes a new `GcCellRef` from a component of the borrowed data.
///
/// The `GcCell` is already immutably borrowed, so this cannot fail.
Expand All @@ -684,7 +701,7 @@ impl<'a, T: Trace + ?Sized> GcCellRef<'a, T> {
#[inline]
pub fn map<U, F>(orig: Self, f: F) -> GcCellRef<'a, U>
where
U: Trace + ?Sized,
U: ?Sized,
F: FnOnce(&T) -> &U,
{
let ret = GcCellRef {
Expand Down Expand Up @@ -720,8 +737,8 @@ impl<'a, T: Trace + ?Sized> GcCellRef<'a, T> {
#[inline]
pub fn map_split<U, V, F>(orig: Self, f: F) -> (GcCellRef<'a, U>, GcCellRef<'a, V>)
where
U: Trace + ?Sized,
V: Trace + ?Sized,
U: ?Sized,
V: ?Sized,
F: FnOnce(&T) -> (&U, &V),
{
let (a, b) = f(orig.value);
Expand All @@ -747,7 +764,7 @@ impl<'a, T: Trace + ?Sized> GcCellRef<'a, T> {
}
}

impl<'a, T: Trace + ?Sized> Deref for GcCellRef<'a, T> {
impl<'a, T: ?Sized> Deref for GcCellRef<'a, T> {
type Target = T;

#[inline]
Expand All @@ -756,20 +773,20 @@ impl<'a, T: Trace + ?Sized> Deref for GcCellRef<'a, T> {
}
}

impl<'a, T: Trace + ?Sized> Drop for GcCellRef<'a, T> {
impl<'a, T: ?Sized> Drop for GcCellRef<'a, T> {
fn drop(&mut self) {
debug_assert!(self.flags.get().borrowed() == BorrowState::Reading);
self.flags.set(self.flags.get().sub_reading());
}
}

impl<'a, T: Trace + ?Sized + Debug> Debug for GcCellRef<'a, T> {
impl<'a, T: ?Sized + Debug> Debug for GcCellRef<'a, T> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
Debug::fmt(&**self, f)
}
}

impl<'a, T: Trace + ?Sized + Display> Display for GcCellRef<'a, T> {
impl<'a, T: ?Sized + Display> Display for GcCellRef<'a, T> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
Display::fmt(&**self, f)
}
Expand Down