1 // Copyright 2012 The Rust Project Developers. See the COPYRIGHT
2 // file at the top-level directory of this distribution and at
3 // http://rust-lang.org/COPYRIGHT.
5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
8 // option. This file may not be copied, modified, or distributed
9 // except according to those terms.
11 use super::combine::CombineFields;
13 use super::lattice::{self, LatticeDir};
16 use traits::ObligationCause;
17 use ty::{self, Ty, TyCtxt};
18 use ty::relate::{Relate, RelateResult, TypeRelation};
20 /// "Greatest lower bound" (common subtype)
21 pub struct Glb<'combine, 'infcx: 'combine, 'gcx: 'infcx+'tcx, 'tcx: 'infcx> {
22 fields: &'combine mut CombineFields<'infcx, 'gcx, 'tcx>,
26 impl<'combine, 'infcx, 'gcx, 'tcx> Glb<'combine, 'infcx, 'gcx, 'tcx> {
27 pub fn new(fields: &'combine mut CombineFields<'infcx, 'gcx, 'tcx>, a_is_expected: bool)
28 -> Glb<'combine, 'infcx, 'gcx, 'tcx>
30 Glb { fields: fields, a_is_expected: a_is_expected }
34 impl<'combine, 'infcx, 'gcx, 'tcx> TypeRelation<'infcx, 'gcx, 'tcx>
35 for Glb<'combine, 'infcx, 'gcx, 'tcx>
37 fn tag(&self) -> &'static str { "Glb" }
39 fn tcx(&self) -> TyCtxt<'infcx, 'gcx, 'tcx> { self.fields.tcx() }
41 fn a_is_expected(&self) -> bool { self.a_is_expected }
43 fn relate_with_variance<T: Relate<'tcx>>(&mut self,
44 variance: ty::Variance,
47 -> RelateResult<'tcx, T>
50 ty::Invariant => self.fields.equate(self.a_is_expected).relate(a, b),
51 ty::Covariant => self.relate(a, b),
52 // FIXME(#41044) -- not correct, need test
53 ty::Bivariant => Ok(a.clone()),
54 ty::Contravariant => self.fields.lub(self.a_is_expected).relate(a, b),
58 fn tys(&mut self, a: Ty<'tcx>, b: Ty<'tcx>) -> RelateResult<'tcx, Ty<'tcx>> {
59 lattice::super_lattice_tys(self, a, b)
62 fn regions(&mut self, a: ty::Region<'tcx>, b: ty::Region<'tcx>)
63 -> RelateResult<'tcx, ty::Region<'tcx>> {
64 debug!("{}.regions({:?}, {:?})",
69 let origin = Subtype(self.fields.trace.clone());
70 Ok(self.fields.infcx.borrow_region_constraints().glb_regions(self.tcx(), origin, a, b))
73 fn binders<T>(&mut self, a: &ty::Binder<T>, b: &ty::Binder<T>)
74 -> RelateResult<'tcx, ty::Binder<T>>
77 debug!("binders(a={:?}, b={:?})", a, b);
79 // When higher-ranked types are involved, computing the LUB is
80 // very challenging, switch to invariance. This is obviously
81 // overly conservative but works ok in practice.
82 self.relate_with_variance(ty::Variance::Invariant, a, b)?;
87 impl<'combine, 'infcx, 'gcx, 'tcx> LatticeDir<'infcx, 'gcx, 'tcx>
88 for Glb<'combine, 'infcx, 'gcx, 'tcx>
90 fn infcx(&self) -> &'infcx InferCtxt<'infcx, 'gcx, 'tcx> {
94 fn cause(&self) -> &ObligationCause<'tcx> {
95 &self.fields.trace.cause
98 fn relate_bound(&mut self, v: Ty<'tcx>, a: Ty<'tcx>, b: Ty<'tcx>) -> RelateResult<'tcx, ()> {
99 let mut sub = self.fields.sub(self.a_is_expected);