src/librustc/infer/equate.rs

   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 ty::{self, Ty, TyCtxt};
  17 use ty::TyVar;
  18 use ty::relate::{Relate, RelateResult, TypeRelation};
  19 use traits::PredicateObligations;
  20
  21 /// Ensures `a` is made equal to `b`. Returns `a` on success.
  22 pub struct Equate<'a, 'tcx: 'a> {
  23     fields: CombineFields<'a, 'tcx>
  24 }
  25
  26 impl<'a, 'tcx> Equate<'a, 'tcx> {
  27     pub fn new(fields: CombineFields<'a, 'tcx>) -> Equate<'a, 'tcx> {
  28         Equate { fields: fields }
  29     }
  30
  31     pub fn obligations(self) -> PredicateObligations<'tcx> {
  32         self.fields.obligations
  33     }
  34 }
  35
  36 impl<'a, 'tcx> TypeRelation<'a,'tcx> for Equate<'a, 'tcx> {
  37     fn tag(&self) -> &'static str { "Equate" }
  38
  39     fn tcx(&self) -> &'a TyCtxt<'tcx> { self.fields.tcx() }
  40
  41     fn a_is_expected(&self) -> bool { self.fields.a_is_expected }
  42
  43     fn relate_with_variance<T:Relate<'a,'tcx>>(&mut self,
  44                                                _: ty::Variance,
  45                                                a: &T,
  46                                                b: &T)
  47                                                -> RelateResult<'tcx, T>
  48     {
  49         self.relate(a, b)
  50     }
  51
  52     fn tys(&mut self, a: Ty<'tcx>, b: Ty<'tcx>) -> RelateResult<'tcx, Ty<'tcx>> {
  53         debug!("{}.tys({:?}, {:?})", self.tag(),
  54                a, b);
  55         if a == b { return Ok(a); }
  56
  57         let infcx = self.fields.infcx;
  58         let a = infcx.type_variables.borrow_mut().replace_if_possible(a);
  59         let b = infcx.type_variables.borrow_mut().replace_if_possible(b);
  60         match (&a.sty, &b.sty) {
  61             (&ty::TyInfer(TyVar(a_id)), &ty::TyInfer(TyVar(b_id))) => {
  62                 infcx.type_variables.borrow_mut().relate_vars(a_id, EqTo, b_id);
  63                 Ok(a)
  64             }
  65
  66             (&ty::TyInfer(TyVar(a_id)), _) => {
  67                 self.fields.instantiate(b, EqTo, a_id)?;
  68                 Ok(a)
  69             }
  70
  71             (_, &ty::TyInfer(TyVar(b_id))) => {
  72                 self.fields.instantiate(a, EqTo, b_id)?;
  73                 Ok(a)
  74             }
  75
  76             _ => {
  77                 combine::super_combine_tys(self.fields.infcx, self, a, b)?;
  78                 Ok(a)
  79             }
  80         }
  81     }
  82
  83     fn regions(&mut self, a: ty::Region, b: ty::Region) -> RelateResult<'tcx, ty::Region> {
  84         debug!("{}.regions({:?}, {:?})",
  85                self.tag(),
  86                a,
  87                b);
  88         let origin = Subtype(self.fields.trace.clone());
  89         self.fields.infcx.region_vars.make_eqregion(origin, a, b);
  90         Ok(a)
  91     }
  92
  93     fn binders<T>(&mut self, a: &ty::Binder<T>, b: &ty::Binder<T>)
  94                   -> RelateResult<'tcx, ty::Binder<T>>
  95         where T: Relate<'a, 'tcx>
  96     {
  97         self.fields.higher_ranked_sub(a, b)?;
  98         self.fields.higher_ranked_sub(b, a)
  99     }
 100 }