96 lines
3.4 KiB
Rust
96 lines
3.4 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 middle::ty::{self, Ty};
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use middle::ty_relate::{self, Relate, TypeRelation, RelateResult};
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/// A type "A" *matches* "B" if the fresh types in B could be
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/// substituted with values so as to make it equal to A. Matching is
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/// intended to be used only on freshened types, and it basically
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/// indicates if the non-freshened versions of A and B could have been
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/// unified.
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///
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/// It is only an approximation. If it yields false, unification would
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/// definitely fail, but a true result doesn't mean unification would
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/// succeed. This is because we don't track the "side-constraints" on
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/// type variables, nor do we track if the same freshened type appears
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/// more than once. To some extent these approximations could be
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/// fixed, given effort.
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///
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/// Like subtyping, matching is really a binary relation, so the only
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/// important thing about the result is Ok/Err. Also, matching never
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/// affects any type variables or unification state.
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pub struct Match<'a, 'tcx: 'a> {
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tcx: &'a ty::ctxt<'tcx>
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}
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impl<'a, 'tcx> Match<'a, 'tcx> {
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pub fn new(tcx: &'a ty::ctxt<'tcx>) -> Match<'a, 'tcx> {
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Match { tcx: tcx }
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}
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}
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impl<'a, 'tcx> TypeRelation<'a, 'tcx> for Match<'a, 'tcx> {
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fn tag(&self) -> &'static str { "Match" }
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fn tcx(&self) -> &'a ty::ctxt<'tcx> { self.tcx }
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fn a_is_expected(&self) -> bool { true } // irrelevant
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fn relate_with_variance<T:Relate<'a,'tcx>>(&mut self,
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_: 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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self.relate(a, b)
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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,
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b);
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Ok(a)
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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(),
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a, b);
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if a == b { return Ok(a); }
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match (&a.sty, &b.sty) {
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(_, &ty::TyInfer(ty::FreshTy(_))) |
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(_, &ty::TyInfer(ty::FreshIntTy(_))) |
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(_, &ty::TyInfer(ty::FreshFloatTy(_))) => {
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Ok(a)
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}
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(&ty::TyInfer(_), _) |
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(_, &ty::TyInfer(_)) => {
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Err(ty::TypeError::Sorts(ty_relate::expected_found(self, &a, &b)))
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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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ty_relate::super_relate_tys(self, a, b)
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}
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}
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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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Ok(ty::Binder(try!(self.relate(a.skip_binder(), b.skip_binder()))))
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}
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}
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