# 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.

## Fields§

§`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> DynSend for Steal<T>
where T: DynSend,

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### impl<T> DynSync for Steal<T>
where T: DynSend + DynSync,

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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>
where T: Send + Sync,

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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> Pointable for T

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#### const ALIGN: usize = _

The alignment of pointer.
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#### type Init = T

The type for initializers.
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#### unsafe fn init(init: <T as Pointable>::Init) -> usize

Initializes a with the given initializer. Read more
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#### unsafe fn deref<'a>(ptr: usize) -> &'a T

Dereferences the given pointer. Read more
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#### unsafe fn deref_mut<'a>(ptr: usize) -> &'a mut T

Mutably dereferences the given pointer. Read more
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#### unsafe fn drop(ptr: usize)

Drops the object pointed to by the given pointer. Read more
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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.