Struct rustc_data_structures::steal::Steal

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

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§value: RwLock<Option<T>>

Implementations§

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impl<T> Steal<T>

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pub fn new(value: T) -> Self

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

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pub fn get_mut(&mut self) -> &mut T

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pub fn steal(&self) -> T

Trait Implementations§

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impl<T: Debug> Debug for Steal<T>

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fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter. Read more
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impl<CTX, T: HashStable<CTX>> HashStable<CTX> for Steal<T>

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fn hash_stable(&self, hcx: &mut CTX, hasher: &mut StableHasher)

Auto Trait Implementations§

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impl<T> !Freeze for Steal<T>

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impl<T> !RefUnwindSafe for Steal<T>

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impl<T> Send for Steal<T>
where T: Send,

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impl<T> !Sync for Steal<T>

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impl<T> Unpin for Steal<T>
where T: Unpin,

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impl<T> UnwindSafe for Steal<T>
where T: UnwindSafe,

Blanket Implementations§

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impl<T> Aligned for T

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const ALIGN: Alignment = const ALIGN: Alignment = Alignment::of::<Self>();

Alignment of Self.
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impl<T> Any for T
where T: 'static + ?Sized,

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fn type_id(&self) -> TypeId

Gets the TypeId of self. Read more
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impl<T> Borrow<T> for T
where T: ?Sized,

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fn borrow(&self) -> &T

Immutably borrows from an owned value. Read more
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impl<T> BorrowMut<T> for T
where T: ?Sized,

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fn borrow_mut(&mut self) -> &mut T

Mutably borrows from an owned value. Read more
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impl<T> From<T> for T

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fn from(t: T) -> T

Returns the argument unchanged.

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impl<T> Instrument for T

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fn instrument(self, span: Span) -> Instrumented<Self>

Instruments this type with the provided Span, returning an Instrumented wrapper. Read more
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fn in_current_span(self) -> Instrumented<Self>

Instruments this type with the current Span, returning an Instrumented wrapper. Read more
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impl<T, U> Into<U> for T
where U: From<T>,

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fn into(self) -> U

Calls U::from(self).

That is, this conversion is whatever the implementation of From<T> for U chooses to do.

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

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type Error = Infallible

The type returned in the event of a conversion error.
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fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>

Performs the conversion.
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impl<T, U> TryInto<U> for T
where U: TryFrom<T>,

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

The type returned in the event of a conversion error.
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fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>

Performs the conversion.
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impl<T> WithSubscriber for T

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fn with_subscriber<S>(self, subscriber: S) -> WithDispatch<Self>
where S: Into<Dispatch>,

Attaches the provided Subscriber to this type, returning a WithDispatch wrapper. Read more
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fn with_current_subscriber(self) -> WithDispatch<Self>

Attaches the current default Subscriber to this type, returning a WithDispatch wrapper. Read more
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impl<'a, T> Captures<'a> for T
where T: ?Sized,

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.