98 lines
3.3 KiB
Rust
98 lines
3.3 KiB
Rust
// Copyright 2012 The Rust Project Developers. See the COPYRIGHT
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// file at the top-level directory of this distribution and at
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// http://rust-lang.org/COPYRIGHT.
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//
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// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
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// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
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// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
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// option. This file may not be copied, modified, or distributed
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// except according to those terms.
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use super::combine::CombineFields;
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use super::InferCtxt;
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use super::lattice::{self, LatticeDir};
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use super::Subtype;
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use traits::ObligationCause;
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use ty::{self, Ty, TyCtxt};
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use ty::relate::{Relate, RelateResult, TypeRelation};
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/// "Least upper bound" (common supertype)
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pub struct Lub<'combine, 'infcx: 'combine, 'gcx: 'infcx+'tcx, 'tcx: 'infcx> {
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fields: &'combine mut CombineFields<'infcx, 'gcx, 'tcx>,
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a_is_expected: bool,
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}
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impl<'combine, 'infcx, 'gcx, 'tcx> Lub<'combine, 'infcx, 'gcx, 'tcx> {
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pub fn new(fields: &'combine mut CombineFields<'infcx, 'gcx, 'tcx>, a_is_expected: bool)
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-> Lub<'combine, 'infcx, 'gcx, 'tcx>
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{
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Lub { fields: fields, a_is_expected: a_is_expected }
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}
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}
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impl<'combine, 'infcx, 'gcx, 'tcx> TypeRelation<'infcx, 'gcx, 'tcx>
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for Lub<'combine, 'infcx, 'gcx, 'tcx>
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{
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fn tag(&self) -> &'static str { "Lub" }
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fn tcx(&self) -> TyCtxt<'infcx, 'gcx, 'tcx> { self.fields.tcx() }
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fn a_is_expected(&self) -> bool { self.a_is_expected }
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fn relate_with_variance<T: Relate<'tcx>>(&mut self,
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variance: ty::Variance,
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a: &T,
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b: &T)
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-> RelateResult<'tcx, T>
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{
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match variance {
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ty::Invariant => self.fields.equate(self.a_is_expected).relate(a, b),
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ty::Covariant => self.relate(a, b),
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ty::Bivariant => self.fields.bivariate(self.a_is_expected).relate(a, b),
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ty::Contravariant => self.fields.glb(self.a_is_expected).relate(a, b),
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}
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}
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fn tys(&mut self, a: Ty<'tcx>, b: Ty<'tcx>) -> RelateResult<'tcx, Ty<'tcx>> {
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lattice::super_lattice_tys(self, a, b)
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}
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fn regions(&mut self, a: &'tcx ty::Region, b: &'tcx ty::Region)
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-> RelateResult<'tcx, &'tcx ty::Region> {
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debug!("{}.regions({:?}, {:?})",
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self.tag(),
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a,
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b);
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let origin = Subtype(self.fields.trace.clone());
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Ok(self.fields.infcx.region_vars.lub_regions(origin, a, b))
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}
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fn binders<T>(&mut self, a: &ty::Binder<T>, b: &ty::Binder<T>)
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-> RelateResult<'tcx, ty::Binder<T>>
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where T: Relate<'tcx>
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{
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self.fields.higher_ranked_lub(a, b, self.a_is_expected)
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}
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}
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impl<'combine, 'infcx, 'gcx, 'tcx> LatticeDir<'infcx, 'gcx, 'tcx>
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for Lub<'combine, 'infcx, 'gcx, 'tcx>
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{
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fn infcx(&self) -> &'infcx InferCtxt<'infcx, 'gcx, 'tcx> {
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self.fields.infcx
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}
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fn cause(&self) -> &ObligationCause<'tcx> {
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&self.fields.trace.cause
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}
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fn relate_bound(&mut self, v: Ty<'tcx>, a: Ty<'tcx>, b: Ty<'tcx>) -> RelateResult<'tcx, ()> {
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let mut sub = self.fields.sub(self.a_is_expected);
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sub.relate(&a, &v)?;
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sub.relate(&b, &v)?;
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Ok(())
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}
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}
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