# Struct rustc_mir_build::build::scope::DropTree

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    struct DropTree {
        drops: IndexVec<DropIdx, (DropData, DropIdx)>,
        previous_drops: FxHashMap<(DropIdx, Local, DropKind), DropIdx>,
        entry_points: Vec<(DropIdx, BasicBlock)>,
    }

Expand description

A tree of drops that we have deferred lowering. It’s used for:

- Drops on unwind paths
- Drops on coroutine drop paths (when a suspended coroutine is dropped)
- Drops on return and loop exit paths
- Drops on the else path in an `if let` chain

Once no more nodes could be added to the tree, we lower it to MIR in one go in `build_mir`.

## Fields§

§`drops: IndexVec<DropIdx, (DropData, DropIdx)>`

Drops in the tree.

§`previous_drops: FxHashMap<(DropIdx, Local, DropKind), DropIdx>`

Map for finding the inverse of the `next_drop` relation:

`previous_drops[(drops[i].1, drops[i].0.local, drops[i].0.kind)] == i`

§`entry_points: Vec<(DropIdx, BasicBlock)>`

Edges into the `DropTree` that need to be added once it’s lowered.

## Implementations§

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### impl DropTree

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#### fn new() -> Self

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#### fn add_drop(&mut self, drop: DropData, next: DropIdx) -> DropIdx

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#### fn add_entry(&mut self, from: BasicBlock, to: DropIdx)

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#### fn build_mir<'tcx, T: DropTreeBuilder<'tcx>>( &mut self, cfg: &mut CFG<'tcx>, blocks: &mut IndexVec<DropIdx, Option<BasicBlock>> )

Builds the MIR for a given drop tree.

`blocks` should have the same length as `self.drops`, and may have its first value set to some already existing block.

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#### fn assign_blocks<'tcx, T: DropTreeBuilder<'tcx>>( &mut self, cfg: &mut CFG<'tcx>, blocks: &mut IndexVec<DropIdx, Option<BasicBlock>> )

Assign blocks for all of the drops in the drop tree that need them.

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#### fn link_blocks<'tcx>( &self, cfg: &mut CFG<'tcx>, blocks: &IndexSlice<DropIdx, Option<BasicBlock>> )

## Trait Implementations§

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### impl Debug for DropTree

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

Formats the value using the given formatter. Read more

## Auto Trait Implementations§

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### impl RefUnwindSafe for DropTree

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### impl Send for DropTree

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### impl Sync for DropTree

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### impl Unpin for DropTree

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### impl UnwindSafe for DropTree

## Blanket Implementations§

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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, 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.

## Layout§

Note: Most layout information is completely unstable and may even differ between compilations. The only exception is types with certain `repr(...)` attributes. Please see the Rust Reference's “Type Layout” chapter for details on type layout guarantees.

Size: 80 bytes