Struct rustc_infer::infer::nll_relate::TypeGeneralizer

struct TypeGeneralizer<'me, 'tcx, D> where
    D: TypeRelatingDelegate<'tcx>,  {
    infcx: &'me InferCtxt<'me, 'tcx>,
    delegate: &'me mut D,
    ambient_variance: Variance,
    first_free_index: DebruijnIndex,
    for_vid_sub_root: TyVid,
    universe: UniverseIndex,
}

The “type generalizer” is used when handling inference variables.

The basic strategy for handling a constraint like ?A <: B is to apply a “generalization strategy” to the type B – this replaces all the lifetimes in the type B with fresh inference variables. (You can read more about the strategy in this blog post.)

As an example, if we had ?A <: &'x u32, we would generalize &'x u32 to &'0 u32 where '0 is a fresh variable. This becomes the value of A. Finally, we relate &'0 u32 <: &'x u32, which establishes '0: 'x as a constraint.

As a side-effect of this generalization procedure, we also replace all the bound regions that we have traversed with concrete values, so that the resulting generalized type is independent from the scopes.

Fields

infcx: &'me InferCtxt<'me, 'tcx>

delegate: &'me mut D

ambient_variance: Variance

After we generalize this type, we are going to relative it to some other type. What will be the variance at this point?

first_free_index: DebruijnIndex

for_vid_sub_root: TyVid

The vid of the type variable that is in the process of being instantiated. If we find this within the value we are folding, that means we would have created a cyclic value.

universe: UniverseIndex

The universe of the type variable that is in the process of being instantiated. If we find anything that this universe cannot name, we reject the relation.

Trait Implementations

impl<D, 'tcx, 'me> TypeRelation<'tcx> for TypeGeneralizer<'me, 'tcx, D> where
    D: TypeRelatingDelegate<'tcx>, 

fn tcx(&self) -> TyCtxt<'tcx>

fn param_env(&self) -> ParamEnv<'tcx>

fn tag(&self) -> &'static str

Returns a static string we can use for printouts.

fn a_is_expected(&self) -> bool

Returns true if the value a is the “expected” type in the relation. Just affects error messages.

fn relate_with_variance<T: Relate<'tcx>>(
    &mut self,
    variance: Variance,
    a: T,
    b: T
) -> RelateResult<'tcx, T>

Switch variance for the purpose of relating a and b.

fn tys(&mut self, a: Ty<'tcx>, _: Ty<'tcx>) -> RelateResult<'tcx, Ty<'tcx>>

fn regions(
    &mut self,
    a: Region<'tcx>,
    _: Region<'tcx>
) -> RelateResult<'tcx, Region<'tcx>>

fn consts(
    &mut self,
    a: &'tcx Const<'tcx>,
    _: &'tcx Const<'tcx>
) -> RelateResult<'tcx, &'tcx Const<'tcx>>

fn binders<T>(
    &mut self,
    a: Binder<T>,
    _: Binder<T>
) -> RelateResult<'tcx, Binder<T>> where
    T: Relate<'tcx>, 

pub fn visit_ct_substs(&self) -> bool

Whether we should look into the substs of unevaluated constants even if feature(const_evaluatable_checked) is active.

pub fn with_cause<F, R>(&mut self, _cause: Cause, f: F) -> R where
    F: FnOnce(&mut Self) -> R, 

pub fn relate<T>(&mut self, a: T, b: T) -> Result<T, TypeError<'tcx>> where
    T: Relate<'tcx>, 

Generic relation routine suitable for most anything.

pub fn relate_item_substs(
    &mut self,
    item_def_id: DefId,
    a_subst: &'tcx List<GenericArg<'tcx>>,
    b_subst: &'tcx List<GenericArg<'tcx>>
) -> Result<&'tcx List<GenericArg<'tcx>>, TypeError<'tcx>>

Relate the two substitutions for the given item. The default is to look up the variance for the item and proceed accordingly.