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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.
4 //
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.
10
11 use super::combine::CombineFields;
12 use super::higher_ranked::HigherRankedRelations;
13 use super::InferCtxt;
14 use super::lattice::{self, LatticeDir};
15 use super::Subtype;
16
17 use middle::ty::{self, Ty};
18 use middle::ty::relate::{Relate, RelateResult, TypeRelation};
19
20 /// "Greatest lower bound" (common subtype)
21 pub struct Glb<'a, 'tcx: 'a> {
22 fields: CombineFields<'a, 'tcx>
23 }
24
25 impl<'a, 'tcx> Glb<'a, 'tcx> {
26 pub fn new(fields: CombineFields<'a, 'tcx>) -> Glb<'a, 'tcx> {
27 Glb { fields: fields }
28 }
29 }
30
31 impl<'a, 'tcx> TypeRelation<'a, 'tcx> for Glb<'a, 'tcx> {
32 fn tag(&self) -> &'static str { "Glb" }
33
34 fn tcx(&self) -> &'a ty::ctxt<'tcx> { self.fields.tcx() }
35
36 fn a_is_expected(&self) -> bool { self.fields.a_is_expected }
37
38 fn relate_with_variance<T:Relate<'a,'tcx>>(&mut self,
39 variance: ty::Variance,
40 a: &T,
41 b: &T)
42 -> RelateResult<'tcx, T>
43 {
44 match variance {
45 ty::Invariant => self.fields.equate().relate(a, b),
46 ty::Covariant => self.relate(a, b),
47 ty::Bivariant => self.fields.bivariate().relate(a, b),
48 ty::Contravariant => self.fields.lub().relate(a, b),
49 }
50 }
51
52 fn tys(&mut self, a: Ty<'tcx>, b: Ty<'tcx>) -> RelateResult<'tcx, Ty<'tcx>> {
53 lattice::super_lattice_tys(self, a, b)
54 }
55
56 fn regions(&mut self, a: ty::Region, b: ty::Region) -> RelateResult<'tcx, ty::Region> {
57 debug!("{}.regions({:?}, {:?})",
58 self.tag(),
59 a,
60 b);
61
62 let origin = Subtype(self.fields.trace.clone());
63 Ok(self.fields.infcx.region_vars.glb_regions(origin, a, b))
64 }
65
66 fn binders<T>(&mut self, a: &ty::Binder<T>, b: &ty::Binder<T>)
67 -> RelateResult<'tcx, ty::Binder<T>>
68 where T: Relate<'a, 'tcx>
69 {
70 self.fields.higher_ranked_glb(a, b)
71 }
72 }
73
74 impl<'a, 'tcx> LatticeDir<'a,'tcx> for Glb<'a, 'tcx> {
75 fn infcx(&self) -> &'a InferCtxt<'a,'tcx> {
76 self.fields.infcx
77 }
78
79 fn relate_bound(&self, v: Ty<'tcx>, a: Ty<'tcx>, b: Ty<'tcx>) -> RelateResult<'tcx, ()> {
80 let mut sub = self.fields.sub();
81 try!(sub.relate(&v, &a));
82 try!(sub.relate(&v, &b));
83 Ok(())
84 }
85 }