Struct chalk_ir::fold::Subst

pub struct Subst<'s, 'i, I: Interner> { /* fields omitted */ }

Substitution used during folding

Implementations

impl<I: Interner> Subst<'_, '_, I>

pub fn apply<T: Fold<I>>(
    interner: &I,
    parameters: &[GenericArg<I>],
    value: T
) -> T::Result

Applies the substitution by folding

Trait Implementations

impl<'i, I: Interner> Folder<'i, I> for Subst<'_, 'i, I>

fn fold_free_var_ty(
    &mut self,
    bound_var: BoundVar,
    outer_binder: DebruijnIndex
) -> Fallible<Ty<I>>

We are eliminating one binder, but binders outside of that get preserved.

So e.g. consider this:

for<A, B> { for<C> { [A, C] } }
//          ^ the binder we are substituing with `[u32]`

Here, A would be ^1.0 and C would be ^0.0. We will replace ^0.0 with the 0th index from the list (u32). We will convert ^1.0 (A) to ^0.0 – i.e., shift it out of one level of binder (the for<C> binder we are eliminating).

This gives us as a result:

for<A, B> { [A, u32] }
             ^ represented as `^0.0`

fn fold_free_var_lifetime(
    &mut self,
    bound_var: BoundVar,
    outer_binder: DebruijnIndex
) -> Fallible<Lifetime<I>>

see fold_free_var_ty

fn fold_free_var_const(
    &mut self,
    ty: Ty<I>,
    bound_var: BoundVar,
    outer_binder: DebruijnIndex
) -> Fallible<Const<I>>

see fold_free_var_ty

fn as_dyn(&mut self) -> &mut dyn Folder<'i, I>

Creates a dyn value from this folder. Unfortunately, this must be added manually to each impl of Folder; it permits the default implements below to create a &mut dyn Folder from Self without knowing what Self is (by invoking this method). Effectively, this limits impls of Folder to types for which we are able to create a dyn value (i.e., not [T] types).

fn interner(&self) -> &'i I

Gets the interner that is being folded from.

fn fold_ty(&mut self, ty: Ty<I>, outer_binder: DebruijnIndex) -> Fallible<Ty<I>>

Top-level callback: invoked for each Ty<I> that is encountered when folding. By default, invokes super_fold_with, which will in turn invoke the more specialized folding methods below, like fold_free_var_ty.

fn fold_lifetime(
    &mut self,
    lifetime: Lifetime<I>,
    outer_binder: DebruijnIndex
) -> Fallible<Lifetime<I>>

Top-level callback: invoked for each Lifetime<I> that is encountered when folding. By default, invokes super_fold_with, which will in turn invoke the more specialized folding methods below, like fold_free_var_lifetime.

fn fold_const(
    &mut self,
    constant: Const<I>,
    outer_binder: DebruijnIndex
) -> Fallible<Const<I>>

Top-level callback: invoked for each Const<I> that is encountered when folding. By default, invokes super_fold_with, which will in turn invoke the more specialized folding methods below, like fold_free_var_const.

fn fold_program_clause(
    &mut self,
    clause: ProgramClause<I>,
    outer_binder: DebruijnIndex
) -> Fallible<ProgramClause<I>>

Invoked for every program clause. By default, recursively folds the goals contents.

fn fold_goal(
    &mut self,
    goal: Goal<I>,
    outer_binder: DebruijnIndex
) -> Fallible<Goal<I>>

Invoked for every goal. By default, recursively folds the goals contents.

fn forbid_free_vars(&self) -> bool

If overridden to return true, then folding will panic if a free variable is encountered. This should be done if free type/lifetime variables are not expected.

fn forbid_free_placeholders(&self) -> bool

If overridden to return true, we will panic when a free placeholder type/lifetime/const is encountered.

fn fold_free_placeholder_ty(
    &mut self,
    universe: PlaceholderIndex,
    outer_binder: DebruijnIndex
) -> Fallible<Ty<I>>

Invoked for each occurrence of a placeholder type; these are used when we instantiate binders universally. Returns a type to use instead, which should be suitably shifted to account for binders.

fn fold_free_placeholder_lifetime(
    &mut self,
    universe: PlaceholderIndex,
    outer_binder: DebruijnIndex
) -> Fallible<Lifetime<I>>

As with fold_free_placeholder_ty, but for lifetimes.

fn fold_free_placeholder_const(
    &mut self,
    ty: Ty<I>,
    universe: PlaceholderIndex,
    outer_binder: DebruijnIndex
) -> Fallible<Const<I>>

As with fold_free_placeholder_ty, but for constants.

fn forbid_inference_vars(&self) -> bool

If overridden to return true, inference variables will trigger panics when folded. Used when inference variables are unexpected.

fn fold_inference_ty(
    &mut self,
    var: InferenceVar,
    kind: TyVariableKind,
    outer_binder: DebruijnIndex
) -> Fallible<Ty<I>>

Invoked for each occurrence of a inference type; these are used when we instantiate binders universally. Returns a type to use instead, which should be suitably shifted to account for binders.

fn fold_inference_lifetime(
    &mut self,
    var: InferenceVar,
    outer_binder: DebruijnIndex
) -> Fallible<Lifetime<I>>

As with fold_inference_ty, but for lifetimes.

fn fold_inference_const(
    &mut self,
    ty: Ty<I>,
    var: InferenceVar,
    outer_binder: DebruijnIndex
) -> Fallible<Const<I>>

As with fold_inference_ty, but for constants.