[][src]Struct rustc_middle::ty::steal::Steal

pub struct Steal<T> {
    value: RwLock<Option<T>>,

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.


value: RwLock<Option<T>>


impl<T> Steal<T>[src]

pub fn new(value: T) -> Self[src]

pub fn borrow(&self) -> MappedReadGuard<'_, T>[src]

pub fn steal(&self) -> T[src]

Trait Implementations

impl<'tcx> ArenaAllocatable<'tcx, Steal<Body<'tcx>>> for Steal<Body<'tcx>>[src]

impl<'tcx> ArenaAllocatable<'tcx, Steal<IndexVec<Promoted, Body<'tcx>>>> for Steal<IndexVec<Promoted, Body<'tcx>>>[src]

impl<'a, T> HashStable<StableHashingContext<'a>> for Steal<T> where
    T: HashStable<StableHashingContext<'a>>, 

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

impl<T> Any for T where
    T: 'static + ?Sized

impl<T> Borrow<T> for T where
    T: ?Sized

impl<T> BorrowMut<T> for T where
    T: ?Sized

impl<'a, T> Captures<'a> for T where
    T: ?Sized

impl<T> From<T> for T[src]

impl<T, U> Into<U> for T where
    U: From<T>, 

impl<T> MaybeResult<T> for T[src]

type Error = !

impl<T, U> TryFrom<U> for T where
    U: Into<T>, 

type Error = Infallible

The type returned in the event of a conversion error.

impl<T, U> TryInto<U> for T where
    U: TryFrom<T>, 

type Error = <U as TryFrom<T>>::Error

The type returned in the event of a conversion error.

impl<T> WithConstness for T[src]