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1 // Copyright 2014 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::{self, CombineFields};
12 use super::higher_ranked::HigherRankedRelations;
13 use super::{Subtype};
14 use super::type_variable::{EqTo};
15
16 use middle::ty::{self, Ty};
17 use middle::ty::TyVar;
18 use middle::ty::relate::{Relate, RelateResult, TypeRelation};
19
20 /// Ensures `a` is made equal to `b`. Returns `a` on success.
21 pub struct Equate<'a, 'tcx: 'a> {
22 fields: CombineFields<'a, 'tcx>
23 }
24
25 impl<'a, 'tcx> Equate<'a, 'tcx> {
26 pub fn new(fields: CombineFields<'a, 'tcx>) -> Equate<'a, 'tcx> {
27 Equate { fields: fields }
28 }
29 }
30
31 impl<'a, 'tcx> TypeRelation<'a,'tcx> for Equate<'a, 'tcx> {
32 fn tag(&self) -> &'static str { "Equate" }
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 _: ty::Variance,
40 a: &T,
41 b: &T)
42 -> RelateResult<'tcx, T>
43 {
44 self.relate(a, b)
45 }
46
47 fn tys(&mut self, a: Ty<'tcx>, b: Ty<'tcx>) -> RelateResult<'tcx, Ty<'tcx>> {
48 debug!("{}.tys({:?}, {:?})", self.tag(),
49 a, b);
50 if a == b { return Ok(a); }
51
52 let infcx = self.fields.infcx;
53 let a = infcx.type_variables.borrow().replace_if_possible(a);
54 let b = infcx.type_variables.borrow().replace_if_possible(b);
55 match (&a.sty, &b.sty) {
56 (&ty::TyInfer(TyVar(a_id)), &ty::TyInfer(TyVar(b_id))) => {
57 infcx.type_variables.borrow_mut().relate_vars(a_id, EqTo, b_id);
58 Ok(a)
59 }
60
61 (&ty::TyInfer(TyVar(a_id)), _) => {
62 try!(self.fields.instantiate(b, EqTo, a_id));
63 Ok(a)
64 }
65
66 (_, &ty::TyInfer(TyVar(b_id))) => {
67 try!(self.fields.instantiate(a, EqTo, b_id));
68 Ok(a)
69 }
70
71 _ => {
72 try!(combine::super_combine_tys(self.fields.infcx, self, a, b));
73 Ok(a)
74 }
75 }
76 }
77
78 fn regions(&mut self, a: ty::Region, b: ty::Region) -> RelateResult<'tcx, ty::Region> {
79 debug!("{}.regions({:?}, {:?})",
80 self.tag(),
81 a,
82 b);
83 let origin = Subtype(self.fields.trace.clone());
84 self.fields.infcx.region_vars.make_eqregion(origin, a, b);
85 Ok(a)
86 }
87
88 fn binders<T>(&mut self, a: &ty::Binder<T>, b: &ty::Binder<T>)
89 -> RelateResult<'tcx, ty::Binder<T>>
90 where T: Relate<'a, 'tcx>
91 {
92 try!(self.fields.higher_ranked_sub(a, b));
93 self.fields.higher_ranked_sub(b, a)
94 }
95 }