104 lines
3.6 KiB
Rust
104 lines
3.6 KiB
Rust
// Copyright 2012 The Rust Project Developers. See the COPYRIGHT
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// file at the top-level directory of this distribution and at
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// http://rust-lang.org/COPYRIGHT.
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//
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// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
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// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
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// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
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// option. This file may not be copied, modified, or distributed
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// except according to those terms.
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use super::combine::{self, CombineFields};
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use super::higher_ranked::HigherRankedRelations;
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use super::Subtype;
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use super::type_variable::{SubtypeOf, SupertypeOf};
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use middle::ty::{self, Ty};
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use middle::ty::TyVar;
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use middle::ty_relate::{Relate, RelateResult, TypeRelation};
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use util::ppaux::{Repr};
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/// "Greatest lower bound" (common subtype)
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pub struct Sub<'a, 'tcx: 'a> {
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fields: CombineFields<'a, 'tcx>
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}
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impl<'a, 'tcx> Sub<'a, 'tcx> {
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pub fn new(f: CombineFields<'a, 'tcx>) -> Sub<'a, 'tcx> {
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Sub { fields: f }
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}
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}
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impl<'a, 'tcx> TypeRelation<'a, 'tcx> for Sub<'a, 'tcx> {
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fn tag(&self) -> &'static str { "Sub" }
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fn tcx(&self) -> &'a ty::ctxt<'tcx> { self.fields.infcx.tcx }
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fn a_is_expected(&self) -> bool { self.fields.a_is_expected }
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fn relate_with_variance<T:Relate<'a,'tcx>>(&mut self,
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variance: ty::Variance,
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a: &T,
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b: &T)
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-> RelateResult<'tcx, T>
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{
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match variance {
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ty::Invariant => self.fields.equate().relate(a, b),
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ty::Covariant => self.relate(a, b),
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ty::Bivariant => self.fields.bivariate().relate(a, b),
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ty::Contravariant => self.fields.switch_expected().sub().relate(b, a),
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}
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}
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fn tys(&mut self, a: Ty<'tcx>, b: Ty<'tcx>) -> RelateResult<'tcx, Ty<'tcx>> {
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debug!("{}.tys({}, {})", self.tag(), a.repr(), b.repr());
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if a == b { return Ok(a); }
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let infcx = self.fields.infcx;
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let a = infcx.type_variables.borrow().replace_if_possible(a);
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let b = infcx.type_variables.borrow().replace_if_possible(b);
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match (&a.sty, &b.sty) {
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(&ty::TyInfer(TyVar(a_id)), &ty::TyInfer(TyVar(b_id))) => {
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infcx.type_variables
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.borrow_mut()
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.relate_vars(a_id, SubtypeOf, b_id);
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Ok(a)
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}
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(&ty::TyInfer(TyVar(a_id)), _) => {
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try!(self.fields
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.switch_expected()
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.instantiate(b, SupertypeOf, a_id));
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Ok(a)
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}
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(_, &ty::TyInfer(TyVar(b_id))) => {
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try!(self.fields.instantiate(a, SubtypeOf, b_id));
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Ok(a)
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}
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(&ty::TyError, _) | (_, &ty::TyError) => {
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Ok(self.tcx().types.err)
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}
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_ => {
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combine::super_combine_tys(self.fields.infcx, self, a, b)
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}
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}
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}
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fn regions(&mut self, a: ty::Region, b: ty::Region) -> RelateResult<'tcx, ty::Region> {
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debug!("{}.regions({}, {})",
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self.tag(),
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a.repr(),
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b.repr());
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let origin = Subtype(self.fields.trace.clone());
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self.fields.infcx.region_vars.make_subregion(origin, a, b);
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Ok(a)
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}
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fn binders<T>(&mut self, a: &ty::Binder<T>, b: &ty::Binder<T>)
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-> RelateResult<'tcx, ty::Binder<T>>
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where T: Relate<'a,'tcx>
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{
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self.fields.higher_ranked_sub(a, b)
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}
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}
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