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[rustc.git] / src / librustc / middle / infer / equate.rs
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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
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11use super::combine::{self, CombineFields};
12use super::higher_ranked::HigherRankedRelations;
13use super::{Subtype};
14use super::type_variable::{EqTo};
15
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16use middle::ty::{self, Ty};
17use middle::ty::TyVar;
e9174d1e 18use middle::ty::relate::{Relate, RelateResult, TypeRelation};
1a4d82fc 19
b039eaaf 20/// Ensures `a` is made equal to `b`. Returns `a` on success.
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21pub struct Equate<'a, 'tcx: 'a> {
22 fields: CombineFields<'a, 'tcx>
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23}
24
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25impl<'a, 'tcx> Equate<'a, 'tcx> {
26 pub fn new(fields: CombineFields<'a, 'tcx>) -> Equate<'a, 'tcx> {
27 Equate { fields: fields }
1a4d82fc 28 }
c34b1796 29}
1a4d82fc 30
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31impl<'a, 'tcx> TypeRelation<'a,'tcx> for Equate<'a, 'tcx> {
32 fn tag(&self) -> &'static str { "Equate" }
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 _: ty::Variance,
40 a: &T,
41 b: &T)
42 -> RelateResult<'tcx, T>
1a4d82fc 43 {
c34b1796 44 self.relate(a, b)
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45 }
46
c34b1796 47 fn tys(&mut self, a: Ty<'tcx>, b: Ty<'tcx>) -> RelateResult<'tcx, Ty<'tcx>> {
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48 debug!("{}.tys({:?}, {:?})", self.tag(),
49 a, b);
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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) {
62682a34 56 (&ty::TyInfer(TyVar(a_id)), &ty::TyInfer(TyVar(b_id))) => {
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57 infcx.type_variables.borrow_mut().relate_vars(a_id, EqTo, b_id);
58 Ok(a)
59 }
60
62682a34 61 (&ty::TyInfer(TyVar(a_id)), _) => {
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62 try!(self.fields.instantiate(b, EqTo, a_id));
63 Ok(a)
64 }
65
62682a34 66 (_, &ty::TyInfer(TyVar(b_id))) => {
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67 try!(self.fields.instantiate(a, EqTo, b_id));
68 Ok(a)
69 }
70
71 _ => {
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72 try!(combine::super_combine_tys(self.fields.infcx, self, a, b));
73 Ok(a)
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74 }
75 }
76 }
77
c34b1796 78 fn regions(&mut self, a: ty::Region, b: ty::Region) -> RelateResult<'tcx, ty::Region> {
62682a34 79 debug!("{}.regions({:?}, {:?})",
c34b1796 80 self.tag(),
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81 a,
82 b);
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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>
1a4d82fc 91 {
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92 try!(self.fields.higher_ranked_sub(a, b));
93 self.fields.higher_ranked_sub(b, a)
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94 }
95}