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::*;
12 use super::{cres, CresCompare};
13 use super::equate::Equate;
15 use super::higher_ranked::HigherRankedRelations;
18 use super::{TypeTrace, Subtype};
19 use super::type_variable::{SubtypeOf, SupertypeOf};
21 use middle::ty::{BuiltinBounds};
22 use middle::ty::{mod, Ty};
23 use middle::ty::TyVar;
24 use util::ppaux::{Repr};
26 use syntax::ast::{Onceness, MutImmutable, MutMutable, Unsafety};
29 /// "Greatest lower bound" (common subtype)
30 pub struct Sub<'f, 'tcx: 'f> {
31 fields: CombineFields<'f, 'tcx>
34 #[allow(non_snake_case)]
35 pub fn Sub<'f, 'tcx>(cf: CombineFields<'f, 'tcx>) -> Sub<'f, 'tcx> {
39 impl<'f, 'tcx> Combine<'tcx> for Sub<'f, 'tcx> {
40 fn infcx<'a>(&'a self) -> &'a InferCtxt<'a, 'tcx> { self.fields.infcx }
41 fn tag(&self) -> String { "sub".to_string() }
42 fn a_is_expected(&self) -> bool { self.fields.a_is_expected }
43 fn trace(&self) -> TypeTrace<'tcx> { self.fields.trace.clone() }
45 fn equate<'a>(&'a self) -> Equate<'a, 'tcx> { Equate(self.fields.clone()) }
46 fn sub<'a>(&'a self) -> Sub<'a, 'tcx> { Sub(self.fields.clone()) }
47 fn lub<'a>(&'a self) -> Lub<'a, 'tcx> { Lub(self.fields.clone()) }
48 fn glb<'a>(&'a self) -> Glb<'a, 'tcx> { Glb(self.fields.clone()) }
50 fn contratys(&self, a: Ty<'tcx>, b: Ty<'tcx>) -> cres<'tcx, Ty<'tcx>> {
51 Sub(self.fields.switch_expected()).tys(b, a)
54 fn contraregions(&self, a: ty::Region, b: ty::Region)
55 -> cres<'tcx, ty::Region> {
56 let opp = CombineFields {
57 a_is_expected: !self.fields.a_is_expected,
60 Sub(opp).regions(b, a)
63 fn regions(&self, a: ty::Region, b: ty::Region) -> cres<'tcx, ty::Region> {
64 debug!("{}.regions({}, {})",
68 self.infcx().region_vars.make_subregion(Subtype(self.trace()), a, b);
72 fn mts(&self, a: &ty::mt<'tcx>, b: &ty::mt<'tcx>) -> cres<'tcx, ty::mt<'tcx>> {
73 debug!("mts({} <: {})",
77 if a.mutbl != b.mutbl {
78 return Err(ty::terr_mutability);
83 // If supertype is mut, subtype must match exactly
84 // (i.e., invariant if mut):
85 try!(self.equate().tys(a.ty, b.ty));
88 // Otherwise we can be covariant:
89 try!(self.tys(a.ty, b.ty));
93 Ok(*a) // return is meaningless in sub, just return *a
96 fn unsafeties(&self, a: Unsafety, b: Unsafety) -> cres<'tcx, Unsafety> {
97 self.lub().unsafeties(a, b).compare(b, || {
98 ty::terr_unsafety_mismatch(expected_found(self, a, b))
102 fn oncenesses(&self, a: Onceness, b: Onceness) -> cres<'tcx, Onceness> {
103 self.lub().oncenesses(a, b).compare(b, || {
104 ty::terr_onceness_mismatch(expected_found(self, a, b))
108 fn builtin_bounds(&self, a: BuiltinBounds, b: BuiltinBounds)
109 -> cres<'tcx, BuiltinBounds> {
110 // More bounds is a subtype of fewer bounds.
112 // e.g., fn:Copy() <: fn(), because the former is a function
113 // that only closes over copyable things, but the latter is
114 // any function at all.
115 if a.is_superset(&b) {
118 Err(ty::terr_builtin_bounds(expected_found(self, a, b)))
122 fn tys(&self, a: Ty<'tcx>, b: Ty<'tcx>) -> cres<'tcx, Ty<'tcx>> {
123 debug!("{}.tys({}, {})", self.tag(),
124 a.repr(self.tcx()), b.repr(self.tcx()));
125 if a == b { return Ok(a); }
127 let infcx = self.fields.infcx;
128 let a = infcx.type_variables.borrow().replace_if_possible(a);
129 let b = infcx.type_variables.borrow().replace_if_possible(b);
130 match (&a.sty, &b.sty) {
131 (&ty::ty_infer(TyVar(a_id)), &ty::ty_infer(TyVar(b_id))) => {
134 .relate_vars(a_id, SubtypeOf, b_id);
137 (&ty::ty_infer(TyVar(a_id)), _) => {
140 .instantiate(b, SupertypeOf, a_id));
143 (_, &ty::ty_infer(TyVar(b_id))) => {
144 try!(self.fields.instantiate(a, SubtypeOf, b_id));
148 (&ty::ty_err, _) | (_, &ty::ty_err) => {
149 Ok(self.tcx().types.err)
153 super_tys(self, a, b)
158 fn binders<T>(&self, a: &ty::Binder<T>, b: &ty::Binder<T>) -> cres<'tcx, ty::Binder<T>>
159 where T : Combineable<'tcx>
161 self.higher_ranked_sub(a, b)