# 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

Innermost index.

One level higher than the innermost index.

Creates a new de Bruijn index with a given depth.

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

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`

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

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

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).

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

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

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

Returns a copy of the value. Read more

Performs copy-assignment from `source`. Read more

Formats the value using the given formatter. Read more

Feeds this value into the given `Hasher`. Read more

Feeds a slice of this type into the given `Hasher`. Read more

This method returns an `Ordering` between `self` and `other`. Read more

Compares and returns the maximum of two values. Read more

Compares and returns the minimum of two values. Read more

Restrict a value to a certain interval. Read more

This method tests for `self` and `other` values to be equal, and is used by `==`. Read more

This method tests for `!=`.

This method returns an ordering between `self` and `other` values if one exists. Read more

This method tests less than (for `self` and `other`) and is used by the `<` operator. Read more

This method tests less than or equal to (for `self` and `other`) and is used by the `<=` operator. Read more

This method tests greater than (for `self` and `other`) and is used by the `>` operator. Read more

This method tests greater than or equal to (for `self` and `other`) and is used by the `>=` operator. Read more

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. Read more

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. Read more

## Blanket Implementations

Gets the `TypeId` of `self`. Read more

Immutably borrows from an owned value. Read more

Mutably borrows from an owned value. Read more

Cast a value to type `U` using `CastTo`.

Returns the argument unchanged.

Calls `U::from(self)`.

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

Shifts this term in one level of binders.

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. Read more

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. Read more

Shifts this term out one level of binders.

The resulting type after obtaining ownership.

Creates owned data from borrowed data, usually by cloning. Read more

🔬 This is a nightly-only experimental API. (`toowned_clone_into`)

Uses borrowed data to replace owned data, usually by cloning. Read more

The type returned in the event of a conversion error.

Performs the conversion.

The type returned in the event of a conversion error.

Performs the conversion.

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