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[rustc.git] / src / librustc / middle / infer / glb.rs
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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
c34b1796 11use super::combine::CombineFields;
1a4d82fc 12use super::higher_ranked::HigherRankedRelations;
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13use super::InferCtxt;
14use super::lattice::{self, LatticeDir};
85aaf69f 15use super::Subtype;
1a4d82fc 16
1a4d82fc 17use middle::ty::{self, Ty};
e9174d1e 18use middle::ty::relate::{Relate, RelateResult, TypeRelation};
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19
20/// "Greatest lower bound" (common subtype)
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21pub struct Glb<'a, 'tcx: 'a> {
22 fields: CombineFields<'a, 'tcx>
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23}
24
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25impl<'a, 'tcx> Glb<'a, 'tcx> {
26 pub fn new(fields: CombineFields<'a, 'tcx>) -> Glb<'a, 'tcx> {
27 Glb { fields: fields }
85aaf69f 28 }
c34b1796 29}
85aaf69f 30
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31impl<'a, 'tcx> TypeRelation<'a, 'tcx> for Glb<'a, 'tcx> {
32 fn tag(&self) -> &'static str { "Glb" }
1a4d82fc 33
c34b1796 34 fn tcx(&self) -> &'a ty::ctxt<'tcx> { self.fields.tcx() }
1a4d82fc 35
c34b1796 36 fn a_is_expected(&self) -> bool { self.fields.a_is_expected }
1a4d82fc 37
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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),
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49 }
50 }
51
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52 fn tys(&mut self, a: Ty<'tcx>, b: Ty<'tcx>) -> RelateResult<'tcx, Ty<'tcx>> {
53 lattice::super_lattice_tys(self, a, b)
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54 }
55
c34b1796 56 fn regions(&mut self, a: ty::Region, b: ty::Region) -> RelateResult<'tcx, ty::Region> {
62682a34 57 debug!("{}.regions({:?}, {:?})",
1a4d82fc 58 self.tag(),
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59 a,
60 b);
1a4d82fc 61
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62 let origin = Subtype(self.fields.trace.clone());
63 Ok(self.fields.infcx.region_vars.glb_regions(origin, a, b))
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64 }
65
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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)
1a4d82fc 71 }
c34b1796 72}
1a4d82fc 73
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74impl<'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(())
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84 }
85}