# Struct chalk_ir::DebruijnIndex

``````pub struct DebruijnIndex {
pub(crate) depth: u32,
}``````
Expand description

References the binder at the given depth. The index is a de Bruijn index, so it counts back through the in-scope binders, with 0 being the innermost binder. This is used in impls and the like. For example, if we had a rule like `for<T> { (T: Clone) :- (T: Copy) }`, then `T` would be represented as a `BoundVar(0)` (as the `for` is the innermost binder).

## Fields§

§`depth: u32`

## Implementations§

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### impl DebruijnIndex

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Innermost index.

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#### pub const ONE: DebruijnIndex = _

One level higher than the innermost index.

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#### pub fn new(depth: u32) -> Self

Creates a new de Bruijn index with a given depth.

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#### pub fn depth(self) -> u32

Depth of the De Bruijn index, counting from 0 starting with the innermost binder.

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#### pub fn within(self, outer_binder: DebruijnIndex) -> bool

True if the binder identified by this index is within the binder identified by the index `outer_binder`.

##### §Example

Imagine you have the following binders in scope

``forall<a> forall<b> forall<c>``

then the Debruijn index for `c` would be `0`, the index for `b` would be 1, and so on. Now consider the following calls:

• `c.within(a) = true`
• `b.within(a) = true`
• `a.within(a) = false`
• `a.within(c) = false`
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#### pub fn shifted_in(self) -> DebruijnIndex

Returns the resulting index when this value is moved into through one binder.

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#### pub fn shift_in(&mut self)

Update this index in place by shifting it “in” through `amount` number of binders.

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#### pub fn shifted_in_from(self, outer_binder: DebruijnIndex) -> DebruijnIndex

Adds `outer_binder` levels to the `self` index. Intuitively, this shifts the `self` index, which was valid at the outer binder, so that it is valid at the innermost binder.

Example: Assume that the following binders are in scope:

``````for<A> for<B> for<C> for<D>
^ outer binder``````

Assume further that the `outer_binder` argument is 2, which means that it is referring to the `for<B>` binder (since `D` would be the innermost binder).

This means that `self` is relative to the binder `B` – so if `self` is 0 (`INNERMOST`), then it refers to `B`, and if `self` is 1, then it refers to `A`.

We will return as follows:

• `0.shifted_in_from(2) = 2` – i.e., `B`, when shifted in to the binding level `D`, has index 2
• `1.shifted_in_from(2) = 3` – i.e., `A`, when shifted in to the binding level `D`, has index 3
• `2.shifted_in_from(1) = 3` – here, we changed the `outer_binder` to refer to `C`. Therefore `2` (relative to `C`) refers to `A`, so the result is still 3 (since `A`, relative to the innermost binder, has index 3).
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#### pub fn shifted_out(self) -> Option<DebruijnIndex>

Returns the resulting index when this value is moved out from `amount` number of new binders.

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#### pub fn shift_out(&mut self)

Update in place by shifting out from `amount` binders.

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#### pub fn shifted_out_to( self, outer_binder: DebruijnIndex ) -> Option<DebruijnIndex>

Subtracts `outer_binder` levels from the `self` index. Intuitively, this shifts the `self` index, which was valid at the innermost binder, to one that is valid at the binder `outer_binder`.

This will return `None` if the `self` index is internal to the outer binder (i.e., if `self < outer_binder`).

Example: Assume that the following binders are in scope:

``````for<A> for<B> for<C> for<D>
^ outer binder``````

Assume further that the `outer_binder` argument is 2, which means that it is referring to the `for<B>` binder (since `D` would be the innermost binder).

This means that the result is relative to the binder `B` – so if `self` is 0 (`INNERMOST`), then it refers to `B`, and if `self` is 1, then it refers to `A`.

We will return as follows:

• `1.shifted_out_to(2) = None` – i.e., the binder for `C` can’t be named from the binding level `B`
• `3.shifted_out_to(2) = Some(1)` – i.e., `A`, when shifted out to the binding level `B`, has index 1

## Trait Implementations§

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### impl Clone for DebruijnIndex

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#### fn clone(&self) -> DebruijnIndex

Returns a copy of the value. Read more
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#### fn clone_from(&mut self, source: &Self)

Performs copy-assignment from `source`. Read more
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### impl Debug for DebruijnIndex

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

Formats the value using the given formatter. Read more
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### impl Hash for DebruijnIndex

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#### fn hash<__H: Hasher>(&self, state: &mut __H)

Feeds this value into the given `Hasher`. Read more
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#### fn hash_slice<H>(data: &[Self], state: &mut H)where H: Hasher, Self: Sized,

Feeds a slice of this type into the given `Hasher`. Read more
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### impl Ord for DebruijnIndex

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#### fn cmp(&self, other: &DebruijnIndex) -> Ordering

This method returns an `Ordering` between `self` and `other`. Read more
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#### fn max(self, other: Self) -> Selfwhere Self: Sized,

Compares and returns the maximum of two values. Read more
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#### fn min(self, other: Self) -> Selfwhere Self: Sized,

Compares and returns the minimum of two values. Read more
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#### fn clamp(self, min: Self, max: Self) -> Selfwhere Self: Sized + PartialOrd,

Restrict a value to a certain interval. Read more
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### impl PartialEq for DebruijnIndex

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#### fn eq(&self, other: &DebruijnIndex) -> bool

This method tests for `self` and `other` values to be equal, and is used by `==`.
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#### fn ne(&self, other: &Rhs) -> bool

This method tests for `!=`. The default implementation is almost always sufficient, and should not be overridden without very good reason.
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### impl PartialOrd for DebruijnIndex

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#### fn partial_cmp(&self, other: &DebruijnIndex) -> Option<Ordering>

This method returns an ordering between `self` and `other` values if one exists. Read more
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#### fn lt(&self, other: &Rhs) -> bool

This method tests less than (for `self` and `other`) and is used by the `<` operator. Read more
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#### fn le(&self, other: &Rhs) -> bool

This method tests less than or equal to (for `self` and `other`) and is used by the `<=` operator. Read more
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#### fn gt(&self, other: &Rhs) -> bool

This method tests greater than (for `self` and `other`) and is used by the `>` operator. Read more
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#### fn ge(&self, other: &Rhs) -> bool

This method tests greater than or equal to (for `self` and `other`) and is used by the `>=` operator. Read more
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### impl<I: Interner> TypeFoldable<I> for DebruijnIndex

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#### fn try_fold_with<E>( self, _folder: &mut dyn FallibleTypeFolder<I, Error = E>, _outer_binder: DebruijnIndex ) -> Result<Self, E>

Apply the given folder `folder` to `self`; `binders` is the number of binders that are in scope when beginning the folder. Typically `binders` starts as 0, but is adjusted when we encounter `Binders<T>` in the IR or other similar constructs.
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#### fn fold_with( self, folder: &mut dyn TypeFolder<I>, outer_binder: DebruijnIndex ) -> Self

A convenient alternative to `try_fold_with` for use with infallible folders. Do not override this method, to ensure coherence with `try_fold_with`.
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### impl<I: Interner> TypeVisitable<I> for DebruijnIndex

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#### fn visit_with<B>( &self, _visitor: &mut dyn TypeVisitor<I, BreakTy = B>, _outer_binder: DebruijnIndex ) -> ControlFlow<B>

Apply the given visitor `visitor` to `self`; `binders` is the number of binders that are in scope when beginning the visitor. Typically `binders` starts as 0, but is adjusted when we encounter `Binders<T>` in the IR or other similar constructs.
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## Blanket Implementations§

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### impl<T> Any for Twhere 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 Twhere 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 Twhere 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> Cast for T

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#### fn cast<U>(self, interner: U::Interner) -> Uwhere Self: CastTo<U>, U: HasInterner,

Cast a value to type `U` using `CastTo`.
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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 Twhere 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, I> Shift<I> for Twhere T: TypeFoldable<I>, I: Interner,

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#### fn shifted_in(self, interner: I) -> T

Shifts this term in one level of binders.
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#### fn shifted_in_from(self, interner: I, source_binder: DebruijnIndex) -> T

Shifts a term valid at `outer_binder` so that it is valid at the innermost binder. See `DebruijnIndex::shifted_in_from` for a detailed explanation.
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#### fn shifted_out_to( self, interner: I, target_binder: DebruijnIndex ) -> Result<T, NoSolution>

Shifts a term valid at the innermost binder so that it is valid at `outer_binder`. See `DebruijnIndex::shifted_out_to` for a detailed explanation.
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#### fn shifted_out(self, interner: I) -> Result<T, NoSolution>

Shifts this term out one level of binders.
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### impl<T> ToOwned for Twhere T: Clone,

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#### type Owned = T

The resulting type after obtaining ownership.
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#### fn to_owned(&self) -> T

Creates owned data from borrowed data, usually by cloning. Read more
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#### fn clone_into(&self, target: &mut T)

Uses borrowed data to replace owned data, usually by cloning. Read more
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### impl<T, U> TryFrom<U> for Twhere 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 Twhere 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, I> VisitExt<I> for Twhere I: Interner, T: TypeVisitable<I>,

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#### fn has_free_vars(&self, interner: I) -> bool

Check whether there are free (non-bound) variables.