src/librustc/middle/infer/lub.rs

   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
  11 use super::combine::CombineFields;
  12 use super::higher_ranked::HigherRankedRelations;
  13 use super::InferCtxt;
  14 use super::lattice::{self, LatticeDir};
  15 use super::Subtype;
  16
  17 use middle::ty::{self, Ty};
  18 use middle::ty_relate::{Relate, RelateResult, TypeRelation};
  19
  20 /// "Least upper bound" (common supertype)
  21 pub struct Lub<'a, 'tcx: 'a> {
  22     fields: CombineFields<'a, 'tcx>
  23 }
  24
  25 impl<'a, 'tcx> Lub<'a, 'tcx> {
  26     pub fn new(fields: CombineFields<'a, 'tcx>) -> Lub<'a, 'tcx> {
  27         Lub { fields: fields }
  28     }
  29 }
  30
  31 impl<'a, 'tcx> TypeRelation<'a, 'tcx> for Lub<'a, 'tcx> {
  32     fn tag(&self) -> &'static str { "Lub" }
  33
  34     fn tcx(&self) -> &'a ty::ctxt<'tcx> { self.fields.tcx() }
  35
  36     fn a_is_expected(&self) -> bool { self.fields.a_is_expected }
  37
  38     fn will_change(&mut self, a: bool, b: bool) -> bool {
  39         // result will be 'static if a || b
  40         a || b
  41     }
  42
  43     fn relate_with_variance<T:Relate<'a,'tcx>>(&mut self,
  44                                                variance: ty::Variance,
  45                                                a: &T,
  46                                                b: &T)
  47                                                -> RelateResult<'tcx, T>
  48     {
  49         match variance {
  50             ty::Invariant => self.fields.equate().relate(a, b),
  51             ty::Covariant => self.relate(a, b),
  52             ty::Bivariant => self.fields.bivariate().relate(a, b),
  53             ty::Contravariant => self.fields.glb().relate(a, b),
  54         }
  55     }
  56
  57     fn tys(&mut self, a: Ty<'tcx>, b: Ty<'tcx>) -> RelateResult<'tcx, Ty<'tcx>> {
  58         lattice::super_lattice_tys(self, a, b)
  59     }
  60
  61     fn regions(&mut self, a: ty::Region, b: ty::Region) -> RelateResult<'tcx, ty::Region> {
  62         debug!("{}.regions({:?}, {:?})",
  63                self.tag(),
  64                a,
  65                b);
  66
  67         let origin = Subtype(self.fields.trace.clone());
  68         Ok(self.fields.infcx.region_vars.lub_regions(origin, a, b))
  69     }
  70
  71     fn binders<T>(&mut self, a: &ty::Binder<T>, b: &ty::Binder<T>)
  72                   -> RelateResult<'tcx, ty::Binder<T>>
  73         where T: Relate<'a, 'tcx>
  74     {
  75         self.fields.higher_ranked_lub(a, b)
  76     }
  77 }
  78
  79 impl<'a, 'tcx> LatticeDir<'a,'tcx> for Lub<'a, 'tcx> {
  80     fn infcx(&self) -> &'a InferCtxt<'a,'tcx> {
  81         self.fields.infcx
  82     }
  83
  84     fn relate_bound(&self, v: Ty<'tcx>, a: Ty<'tcx>, b: Ty<'tcx>) -> RelateResult<'tcx, ()> {
  85         let mut sub = self.fields.sub();
  86         try!(sub.relate(&a, &v));
  87         try!(sub.relate(&b, &v));
  88         Ok(())
  89     }
  90 }
  91