Struct rustc_mir::borrow_check::type_check::free_region_relations::UniversalRegionRelations

pub(crate) struct UniversalRegionRelations<'tcx> {
    universal_regions: Rc<UniversalRegions<'tcx>>,
    outlives: TransitiveRelation<RegionVid>,
    inverse_outlives: TransitiveRelation<RegionVid>,
}

Fields

universal_regions: Rc<UniversalRegions<'tcx>>

outlives: TransitiveRelation<RegionVid>

Stores the outlives relations that are known to hold from the implied bounds, in-scope where-clauses, and that sort of thing.

inverse_outlives: TransitiveRelation<RegionVid>

This is the <= relation; that is, if a: b, then b <= a, and we store that here. This is useful when figuring out how to express some local region in terms of external regions our caller will understand.

Implementations

impl<'tcx> UniversalRegionRelations<'tcx>

fn relate_universal_regions(&mut self, fr_a: RegionVid, fr_b: RegionVid)

Records in the outlives_relation (and inverse_outlives_relation) that fr_a: fr_b. Invoked by the builder below.

pub(crate) fn postdom_upper_bound(
    &self,
    fr1: RegionVid,
    fr2: RegionVid
) -> RegionVid

Given two universal regions, returns the postdominating upper-bound (effectively the least upper bound).

(See TransitiveRelation::postdom_upper_bound for details on the postdominating upper bound in general.)

pub(crate) fn non_local_upper_bounds<'a>(
    &'a self,
    fr: &'a RegionVid
) -> Vec<&'a RegionVid>

Finds an “upper bound” for fr that is not local. In other words, returns the smallest (*) known region fr1 that (a) outlives fr and (b) is not local.

(*) If there are multiple competing choices, we return all of them.

pub(crate) fn non_local_upper_bound(&self, fr: RegionVid) -> RegionVid

Returns the “postdominating” bound of the set of non_local_upper_bounds for the given region.

pub(crate) fn non_local_lower_bound(&self, fr: RegionVid) -> Option<RegionVid>

Finds a “lower bound” for fr that is not local. In other words, returns the largest (*) known region fr1 that (a) is outlived by fr and (b) is not local.

(*) If there are multiple competing choices, we pick the “postdominating” one. See TransitiveRelation::postdom_upper_bound for details.

fn non_local_bounds<'a>(
    &self,
    relation: &'a TransitiveRelation<RegionVid>,
    fr0: &'a RegionVid
) -> Vec<&'a RegionVid>

Helper for non_local_upper_bounds and non_local_lower_bounds. Repeatedly invokes postdom_parent until we find something that is not local. Returns None if we never do so.

pub(crate) fn outlives(&self, fr1: RegionVid, fr2: RegionVid) -> bool

Returns true if fr1 is known to outlive fr2.

This will only ever be true for universally quantified regions.

pub(crate) fn regions_outlived_by(&self, fr1: RegionVid) -> Vec<&RegionVid>

Returns a vector of free regions x such that fr1: x is known to hold.

pub(crate) fn known_outlives(
    &self
) -> impl Iterator<Item = (&RegionVid, &RegionVid)>

Returns the non-transitive set of known outlives constraints between free regions.

Trait Implementations

impl<'tcx> Debug for UniversalRegionRelations<'tcx>

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl<'tcx> FreeRegionRelations<'tcx> for UniversalRegionRelations<'tcx>

This trait is used by the impl-trait constraint code to abstract over the FreeRegionMap from lexical regions and UniversalRegions (from NLL)`.

fn sub_free_regions(
    &self,
    _tcx: TyCtxt<'tcx>,
    shorter: Region<'tcx>,
    longer: Region<'tcx>
) -> bool

Tests whether r_a <= r_b. Both must be free regions or 'static.