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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::{self, CombineFields};
1a4d82fc 12use super::higher_ranked::HigherRankedRelations;
62682a34 13use super::SubregionOrigin;
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14use super::type_variable::{SubtypeOf, SupertypeOf};
15
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16use middle::ty::{self, Ty};
17use middle::ty::TyVar;
e9174d1e 18use middle::ty::relate::{Cause, Relate, RelateResult, TypeRelation};
62682a34 19use std::mem;
1a4d82fc 20
b039eaaf 21/// Ensures `a` is made a subtype of `b`. Returns `a` on success.
c34b1796 22pub struct Sub<'a, 'tcx: 'a> {
62682a34 23 fields: CombineFields<'a, 'tcx>,
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24}
25
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26impl<'a, 'tcx> Sub<'a, 'tcx> {
27 pub fn new(f: CombineFields<'a, 'tcx>) -> Sub<'a, 'tcx> {
28 Sub { fields: f }
29 }
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30}
31
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32impl<'a, 'tcx> TypeRelation<'a, 'tcx> for Sub<'a, 'tcx> {
33 fn tag(&self) -> &'static str { "Sub" }
34 fn tcx(&self) -> &'a ty::ctxt<'tcx> { self.fields.infcx.tcx }
35 fn a_is_expected(&self) -> bool { self.fields.a_is_expected }
85aaf69f 36
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37 fn with_cause<F,R>(&mut self, cause: Cause, f: F) -> R
38 where F: FnOnce(&mut Self) -> R
39 {
40 debug!("sub with_cause={:?}", cause);
41 let old_cause = mem::replace(&mut self.fields.cause, Some(cause));
42 let r = f(self);
43 debug!("sub old_cause={:?}", old_cause);
44 self.fields.cause = old_cause;
45 r
46 }
47
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48 fn relate_with_variance<T:Relate<'a,'tcx>>(&mut self,
49 variance: ty::Variance,
50 a: &T,
51 b: &T)
52 -> RelateResult<'tcx, T>
85aaf69f 53 {
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54 match variance {
55 ty::Invariant => self.fields.equate().relate(a, b),
56 ty::Covariant => self.relate(a, b),
57 ty::Bivariant => self.fields.bivariate().relate(a, b),
58 ty::Contravariant => self.fields.switch_expected().sub().relate(b, a),
85aaf69f 59 }
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60 }
61
c34b1796 62 fn tys(&mut self, a: Ty<'tcx>, b: Ty<'tcx>) -> RelateResult<'tcx, Ty<'tcx>> {
62682a34 63 debug!("{}.tys({:?}, {:?})", self.tag(), a, b);
1a4d82fc 64
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65 if a == b { return Ok(a); }
66
67 let infcx = self.fields.infcx;
68 let a = infcx.type_variables.borrow().replace_if_possible(a);
69 let b = infcx.type_variables.borrow().replace_if_possible(b);
70 match (&a.sty, &b.sty) {
62682a34 71 (&ty::TyInfer(TyVar(a_id)), &ty::TyInfer(TyVar(b_id))) => {
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72 infcx.type_variables
73 .borrow_mut()
74 .relate_vars(a_id, SubtypeOf, b_id);
75 Ok(a)
76 }
62682a34 77 (&ty::TyInfer(TyVar(a_id)), _) => {
1a4d82fc 78 try!(self.fields
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79 .switch_expected()
80 .instantiate(b, SupertypeOf, a_id));
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81 Ok(a)
82 }
62682a34 83 (_, &ty::TyInfer(TyVar(b_id))) => {
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84 try!(self.fields.instantiate(a, SubtypeOf, b_id));
85 Ok(a)
86 }
87
62682a34 88 (&ty::TyError, _) | (_, &ty::TyError) => {
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89 Ok(self.tcx().types.err)
90 }
91
92 _ => {
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93 try!(combine::super_combine_tys(self.fields.infcx, self, a, b));
94 Ok(a)
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95 }
96 }
97 }
98
c34b1796 99 fn regions(&mut self, a: ty::Region, b: ty::Region) -> RelateResult<'tcx, ty::Region> {
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100 debug!("{}.regions({:?}, {:?}) self.cause={:?}",
101 self.tag(), a, b, self.fields.cause);
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102 // FIXME -- we have more fine-grained information available
103 // from the "cause" field, we could perhaps give more tailored
104 // error messages.
105 let origin = SubregionOrigin::Subtype(self.fields.trace.clone());
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106 self.fields.infcx.region_vars.make_subregion(origin, a, b);
107 Ok(a)
108 }
109
110 fn binders<T>(&mut self, a: &ty::Binder<T>, b: &ty::Binder<T>)
111 -> RelateResult<'tcx, ty::Binder<T>>
112 where T: Relate<'a,'tcx>
1a4d82fc 113 {
c34b1796 114 self.fields.higher_ranked_sub(a, b)
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115 }
116}