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::CombineFields;
  12 use super::{Subtype};
  13 use super::type_variable::{EqTo};
  14
  15 use ty::{self, Ty, TyCtxt};
  16 use ty::TyVar;
  17 use ty::relate::{Relate, RelateResult, TypeRelation};
  18
  19 /// Ensures `a` is made equal to `b`. Returns `a` on success.
  20 pub struct Equate<'combine, 'infcx: 'combine, 'gcx: 'infcx+'tcx, 'tcx: 'infcx> {
  21     fields: &'combine mut CombineFields<'infcx, 'gcx, 'tcx>,
  22     a_is_expected: bool,
  23 }
  24
  25 impl<'combine, 'infcx, 'gcx, 'tcx> Equate<'combine, 'infcx, 'gcx, 'tcx> {
  26     pub fn new(fields: &'combine mut CombineFields<'infcx, 'gcx, 'tcx>, a_is_expected: bool)
  27         -> Equate<'combine, 'infcx, 'gcx, 'tcx>
  28     {
  29         Equate { fields: fields, a_is_expected: a_is_expected }
  30     }
  31 }
  32
  33 impl<'combine, 'infcx, 'gcx, 'tcx> TypeRelation<'infcx, 'gcx, 'tcx>
  34     for Equate<'combine, 'infcx, 'gcx, 'tcx>
  35 {
  36     fn tag(&self) -> &'static str { "Equate" }
  37
  38     fn tcx(&self) -> TyCtxt<'infcx, 'gcx, 'tcx> { self.fields.tcx() }
  39
  40     fn a_is_expected(&self) -> bool { self.a_is_expected }
  41
  42     fn relate_with_variance<T: Relate<'tcx>>(&mut self,
  43                                              _: ty::Variance,
  44                                              a: &T,
  45                                              b: &T)
  46                                              -> RelateResult<'tcx, T>
  47     {
  48         self.relate(a, b)
  49     }
  50
  51     fn tys(&mut self, a: Ty<'tcx>, b: Ty<'tcx>) -> RelateResult<'tcx, Ty<'tcx>> {
  52         debug!("{}.tys({:?}, {:?})", self.tag(),
  53                a, b);
  54         if a == b { return Ok(a); }
  55
  56         let infcx = self.fields.infcx;
  57         let a = infcx.type_variables.borrow_mut().replace_if_possible(a);
  58         let b = infcx.type_variables.borrow_mut().replace_if_possible(b);
  59         match (&a.sty, &b.sty) {
  60             (&ty::TyInfer(TyVar(a_id)), &ty::TyInfer(TyVar(b_id))) => {
  61                 infcx.type_variables.borrow_mut().relate_vars(a_id, EqTo, b_id);
  62                 Ok(a)
  63             }
  64
  65             (&ty::TyInfer(TyVar(a_id)), _) => {
  66                 self.fields.instantiate(b, EqTo, a_id, self.a_is_expected)?;
  67                 Ok(a)
  68             }
  69
  70             (_, &ty::TyInfer(TyVar(b_id))) => {
  71                 self.fields.instantiate(a, EqTo, b_id, self.a_is_expected)?;
  72                 Ok(a)
  73             }
  74
  75             _ => {
  76                 self.fields.infcx.super_combine_tys(self, a, b)?;
  77                 Ok(a)
  78             }
  79         }
  80     }
  81
  82     fn regions(&mut self, a: &'tcx ty::Region, b: &'tcx ty::Region)
  83                -> RelateResult<'tcx, &'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<'tcx>
  96     {
  97         self.fields.higher_ranked_sub(a, b, self.a_is_expected)?;
  98         self.fields.higher_ranked_sub(b, a, self.a_is_expected)
  99     }
 100 }