Struct rustc_mir::borrow_check::nll::type_check::relate_tys::TypeGeneralizer

struct TypeGeneralizer<'me, 'bccx: 'me, 'gcx: 'tcx, 'tcx: 'bccx> {
    type_rel: &'me TypeRelating<'me, 'bccx, 'gcx, 'tcx>,
    ambient_variance: Variance,
    first_free_index: DebruijnIndex,
    universe: UniverseIndex,
}

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The "type generalize" 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

type_rel: &'me TypeRelating<'me, 'bccx, 'gcx, 'tcx>

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

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ambient_variance: Variance

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

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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

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

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universe: UniverseIndex

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Trait Implementations

impl<'me, 'gcx, 'tcx, 'bbcx> TypeRelation<'me, 'gcx, 'tcx> for TypeGeneralizer<'me, 'bbcx, 'gcx, 'tcx>

fn tcx(&self) -> TyCtxt<'me, 'gcx, 'tcx>

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

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Returns a static string we can use for printouts.

fn a_is_expected(&self) -> bool

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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>

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Switch variance for the purpose of relating a and b.

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

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

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

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

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

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Generic relation routine suitable for most anything.

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

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

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