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.
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.
11 use super::combine
::{self, CombineFields}
;
12 use super::higher_ranked
::HigherRankedRelations
;
13 use super::SubregionOrigin
;
14 use super::type_variable
::{SubtypeOf, SupertypeOf}
;
16 use ty
::{self, Ty, TyCtxt}
;
18 use ty
::relate
::{Cause, Relate, RelateResult, TypeRelation}
;
19 use traits
::PredicateObligations
;
22 /// Ensures `a` is made a subtype of `b`. Returns `a` on success.
23 pub struct Sub
<'a
, 'tcx
: 'a
> {
24 fields
: CombineFields
<'a
, 'tcx
>,
27 impl<'a
, 'tcx
> Sub
<'a
, 'tcx
> {
28 pub fn new(f
: CombineFields
<'a
, 'tcx
>) -> Sub
<'a
, 'tcx
> {
32 pub fn obligations(self) -> PredicateObligations
<'tcx
> {
33 self.fields
.obligations
37 impl<'a
, 'tcx
> TypeRelation
<'a
, 'tcx
> for Sub
<'a
, 'tcx
> {
38 fn tag(&self) -> &'
static str { "Sub" }
39 fn tcx(&self) -> &'a TyCtxt
<'tcx
> { self.fields.infcx.tcx }
40 fn a_is_expected(&self) -> bool { self.fields.a_is_expected }
42 fn with_cause
<F
,R
>(&mut self, cause
: Cause
, f
: F
) -> R
43 where F
: FnOnce(&mut Self) -> R
45 debug
!("sub with_cause={:?}", cause
);
46 let old_cause
= mem
::replace(&mut self.fields
.cause
, Some(cause
));
48 debug
!("sub old_cause={:?}", old_cause
);
49 self.fields
.cause
= old_cause
;
53 fn relate_with_variance
<T
:Relate
<'a
,'tcx
>>(&mut self,
54 variance
: ty
::Variance
,
57 -> RelateResult
<'tcx
, T
>
60 ty
::Invariant
=> self.fields
.equate().relate(a
, b
),
61 ty
::Covariant
=> self.relate(a
, b
),
62 ty
::Bivariant
=> self.fields
.bivariate().relate(a
, b
),
63 ty
::Contravariant
=> self.fields
.switch_expected().sub().relate(b
, a
),
67 fn tys(&mut self, a
: Ty
<'tcx
>, b
: Ty
<'tcx
>) -> RelateResult
<'tcx
, Ty
<'tcx
>> {
68 debug
!("{}.tys({:?}, {:?})", self.tag(), a
, b
);
70 if a
== b { return Ok(a); }
72 let infcx
= self.fields
.infcx
;
73 let a
= infcx
.type_variables
.borrow_mut().replace_if_possible(a
);
74 let b
= infcx
.type_variables
.borrow_mut().replace_if_possible(b
);
75 match (&a
.sty
, &b
.sty
) {
76 (&ty
::TyInfer(TyVar(a_id
)), &ty
::TyInfer(TyVar(b_id
))) => {
79 .relate_vars(a_id
, SubtypeOf
, b_id
);
82 (&ty
::TyInfer(TyVar(a_id
)), _
) => {
85 .instantiate(b
, SupertypeOf
, a_id
)?
;
88 (_
, &ty
::TyInfer(TyVar(b_id
))) => {
89 self.fields
.instantiate(a
, SubtypeOf
, b_id
)?
;
93 (&ty
::TyError
, _
) | (_
, &ty
::TyError
) => {
94 Ok(self.tcx().types
.err
)
98 combine
::super_combine_tys(self.fields
.infcx
, self, a
, b
)?
;
104 fn regions(&mut self, a
: ty
::Region
, b
: ty
::Region
) -> RelateResult
<'tcx
, ty
::Region
> {
105 debug
!("{}.regions({:?}, {:?}) self.cause={:?}",
106 self.tag(), a
, b
, self.fields
.cause
);
107 // FIXME -- we have more fine-grained information available
108 // from the "cause" field, we could perhaps give more tailored
110 let origin
= SubregionOrigin
::Subtype(self.fields
.trace
.clone());
111 self.fields
.infcx
.region_vars
.make_subregion(origin
, a
, b
);
115 fn binders
<T
>(&mut self, a
: &ty
::Binder
<T
>, b
: &ty
::Binder
<T
>)
116 -> RelateResult
<'tcx
, ty
::Binder
<T
>>
117 where T
: Relate
<'a
,'tcx
>
119 self.fields
.higher_ranked_sub(a
, b
)