| // Copyright 2012 The Rust Project Developers. See the COPYRIGHT |
| // file at the top-level directory of this distribution and at |
| // http://rust-lang.org/COPYRIGHT. |
| // |
| // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or |
| // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license |
| // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your |
| // option. This file may not be copied, modified, or distributed |
| // except according to those terms. |
| |
| use ty::{self, Ty, TyCtxt}; |
| use ty::error::TypeError; |
| use ty::relate::{self, Relate, TypeRelation, RelateResult}; |
| |
| /// A type "A" *matches* "B" if the fresh types in B could be |
| /// substituted with values so as to make it equal to A. Matching is |
| /// intended to be used only on freshened types, and it basically |
| /// indicates if the non-freshened versions of A and B could have been |
| /// unified. |
| /// |
| /// It is only an approximation. If it yields false, unification would |
| /// definitely fail, but a true result doesn't mean unification would |
| /// succeed. This is because we don't track the "side-constraints" on |
| /// type variables, nor do we track if the same freshened type appears |
| /// more than once. To some extent these approximations could be |
| /// fixed, given effort. |
| /// |
| /// Like subtyping, matching is really a binary relation, so the only |
| /// important thing about the result is Ok/Err. Also, matching never |
| /// affects any type variables or unification state. |
| pub struct Match<'a, 'gcx: 'a+'tcx, 'tcx: 'a> { |
| tcx: TyCtxt<'a, 'gcx, 'tcx> |
| } |
| |
| impl<'a, 'gcx, 'tcx> Match<'a, 'gcx, 'tcx> { |
| pub fn new(tcx: TyCtxt<'a, 'gcx, 'tcx>) -> Match<'a, 'gcx, 'tcx> { |
| Match { tcx: tcx } |
| } |
| } |
| |
| impl<'a, 'gcx, 'tcx> TypeRelation<'a, 'gcx, 'tcx> for Match<'a, 'gcx, 'tcx> { |
| fn tag(&self) -> &'static str { "Match" } |
| fn tcx(&self) -> TyCtxt<'a, 'gcx, 'tcx> { self.tcx } |
| fn a_is_expected(&self) -> bool { true } // irrelevant |
| |
| fn relate_with_variance<T: Relate<'tcx>>(&mut self, |
| _: ty::Variance, |
| a: &T, |
| b: &T) |
| -> RelateResult<'tcx, T> |
| { |
| self.relate(a, b) |
| } |
| |
| fn regions(&mut self, a: ty::Region<'tcx>, b: ty::Region<'tcx>) |
| -> RelateResult<'tcx, ty::Region<'tcx>> { |
| debug!("{}.regions({:?}, {:?})", |
| self.tag(), |
| a, |
| b); |
| Ok(a) |
| } |
| |
| fn tys(&mut self, a: Ty<'tcx>, b: Ty<'tcx>) -> RelateResult<'tcx, Ty<'tcx>> { |
| debug!("{}.tys({:?}, {:?})", self.tag(), |
| a, b); |
| if a == b { return Ok(a); } |
| |
| match (&a.sty, &b.sty) { |
| (_, &ty::Infer(ty::FreshTy(_))) | |
| (_, &ty::Infer(ty::FreshIntTy(_))) | |
| (_, &ty::Infer(ty::FreshFloatTy(_))) => { |
| Ok(a) |
| } |
| |
| (&ty::Infer(_), _) | |
| (_, &ty::Infer(_)) => { |
| Err(TypeError::Sorts(relate::expected_found(self, &a, &b))) |
| } |
| |
| (&ty::Error, _) | (_, &ty::Error) => { |
| Ok(self.tcx().types.err) |
| } |
| |
| _ => { |
| relate::super_relate_tys(self, a, b) |
| } |
| } |
| } |
| |
| fn binders<T>(&mut self, a: &ty::Binder<T>, b: &ty::Binder<T>) |
| -> RelateResult<'tcx, ty::Binder<T>> |
| where T: Relate<'tcx> |
| { |
| Ok(ty::Binder::bind(self.relate(a.skip_binder(), b.skip_binder())?)) |
| } |
| } |