Struct chalk_ir::fold::Subst

pub struct Subst<'s, I: Interner> {
    parameters: &'s [GenericArg<I>],
    interner: I,
}

Substitution used during folding

Fields

parameters: &'s [GenericArg<I>]

Values to substitute. A reference to a free variable with index i will be mapped to parameters[i] – if i > parameters.len(), then we will leave the variable untouched.

interner: I

Implementations

impl<I: Interner> Subst<'_, I>

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

Applies the substitution by folding

Trait Implementations

impl<'s, I: Interner> FallibleTypeFolder<I> for Subst<'s, I>

type Error = Infallible

The type this folder returns when folding fails. This is commonly NoSolution.

fn as_dyn(&mut self) -> &mut dyn FallibleTypeFolder<I, Error = Self::Error>

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

fn try_fold_ty( &mut self, ty: Ty<I>, outer_binder: DebruijnIndex ) -> Result<Ty<I>, Self::Error>

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

fn try_fold_lifetime( &mut self, lifetime: Lifetime<I>, outer_binder: DebruijnIndex ) -> Result<Lifetime<I>, Self::Error>

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

fn try_fold_const( &mut self, constant: Const<I>, outer_binder: DebruijnIndex ) -> Result<Const<I>, Self::Error>

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

fn try_fold_program_clause( &mut self, clause: ProgramClause<I>, outer_binder: DebruijnIndex ) -> Result<ProgramClause<I>, Self::Error>

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

fn try_fold_goal( &mut self, goal: Goal<I>, outer_binder: DebruijnIndex ) -> Result<Goal<I>, Self::Error>

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 try_fold_free_var_ty( &mut self, bound_var: BoundVar, outer_binder: DebruijnIndex ) -> Result<Ty<I>, Self::Error>

Invoked for TyKind::BoundVar instances that are not bound within the type being folded over:

fn try_fold_free_var_lifetime( &mut self, bound_var: BoundVar, outer_binder: DebruijnIndex ) -> Result<Lifetime<I>, Self::Error>

As try_fold_free_var_ty, but for lifetimes.

fn try_fold_free_var_const( &mut self, ty: Ty<I>, bound_var: BoundVar, outer_binder: DebruijnIndex ) -> Result<Const<I>, Self::Error>

As try_fold_free_var_ty, but for constants.

fn forbid_free_placeholders(&self) -> bool

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

fn try_fold_free_placeholder_ty( &mut self, universe: PlaceholderIndex, outer_binder: DebruijnIndex ) -> Result<Ty<I>, Self::Error>

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 try_fold_free_placeholder_lifetime( &mut self, universe: PlaceholderIndex, outer_binder: DebruijnIndex ) -> Result<Lifetime<I>, Self::Error>

As with try_fold_free_placeholder_ty, but for lifetimes.

fn try_fold_free_placeholder_const( &mut self, ty: Ty<I>, universe: PlaceholderIndex, outer_binder: DebruijnIndex ) -> Result<Const<I>, Self::Error>

As with try_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 try_fold_inference_ty( &mut self, var: InferenceVar, kind: TyVariableKind, outer_binder: DebruijnIndex ) -> Result<Ty<I>, Self::Error>

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 try_fold_inference_lifetime( &mut self, var: InferenceVar, outer_binder: DebruijnIndex ) -> Result<Lifetime<I>, Self::Error>

As with try_fold_inference_ty, but for lifetimes.

fn try_fold_inference_const( &mut self, ty: Ty<I>, var: InferenceVar, outer_binder: DebruijnIndex ) -> Result<Const<I>, Self::Error>

As with try_fold_inference_ty, but for constants.

fn interner(&self) -> I

Gets the interner that is being folded from.

impl<I: Interner> TypeFolder<I> for Subst<'_, I>

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

see fold_free_var_ty

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

see fold_free_var_ty

fn as_dyn(&mut self) -> &mut dyn TypeFolder<I>

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

fn interner(&self) -> I

Gets the interner that is being folded from.

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

As with fold_inference_ty, but for lifetimes.

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

As with fold_inference_ty, but for constants.