Struct rustc_data_structures::steal::Steal
source · Expand description
The Steal
struct is intended to used as the value for a query.
Specifically, we sometimes have queries (cough MIR cough)
where we create a large, complex value that we want to iteratively
update (e.g., optimize). We could clone the value for each
optimization, but that’d be expensive. And yet we don’t just want
to mutate it in place, because that would spoil the idea that
queries are these pure functions that produce an immutable value
(since if you did the query twice, you could observe the mutations).
So instead we have the query produce a &'tcx Steal<mir::Body<'tcx>>
(to be very specific). Now we can read from this
as much as we want (using borrow()
), but you can also
steal()
. Once you steal, any further attempt to read will panic.
Therefore, we know that – assuming no ICE – nobody is observing
the fact that the MIR was updated.
Obviously, whenever you have a query that yields a Steal
value,
you must treat it with caution, and make sure that you know that
– once the value is stolen – it will never be read from again.
Fields
value: RwLock<Option<T>>
Implementations
Trait Implementations
sourceimpl<CTX, T: HashStable<CTX>> HashStable<CTX> for Steal<T>
impl<CTX, T: HashStable<CTX>> HashStable<CTX> for Steal<T>
fn hash_stable(&self, hcx: &mut CTX, hasher: &mut StableHasher)
Auto Trait Implementations
impl<T> !RefUnwindSafe for Steal<T>
impl<T> Send for Steal<T>where
T: Send,
impl<T> !Sync for Steal<T>
impl<T> Unpin for Steal<T>where
T: Unpin,
impl<T> UnwindSafe for Steal<T>where
T: UnwindSafe,
Blanket Implementations
sourceimpl<T> BorrowMut<T> for Twhere
T: ?Sized,
impl<T> BorrowMut<T> for Twhere
T: ?Sized,
const: unstable · sourcefn borrow_mut(&mut self) -> &mut T
fn borrow_mut(&mut self) -> &mut T
impl<'a, T> Captures<'a> for Twhere
T: ?Sized,
impl<T> Erased for T
Layout
Note: Unable to compute type layout, possibly due to this type having generic parameters. Layout can only be computed for concrete, fully-instantiated types.