1 use crate::ty::{self, Ty, TyCtxt};
2 use crate::ty::error::TypeError;
3 use crate::ty::relate::{self, Relate, TypeRelation, RelateResult};
5 /// A type "A" *matches* "B" if the fresh types in B could be
6 /// substituted with values so as to make it equal to A. Matching is
7 /// intended to be used only on freshened types, and it basically
8 /// indicates if the non-freshened versions of A and B could have been
11 /// It is only an approximation. If it yields false, unification would
12 /// definitely fail, but a true result doesn't mean unification would
13 /// succeed. This is because we don't track the "side-constraints" on
14 /// type variables, nor do we track if the same freshened type appears
15 /// more than once. To some extent these approximations could be
16 /// fixed, given effort.
18 /// Like subtyping, matching is really a binary relation, so the only
19 /// important thing about the result is Ok/Err. Also, matching never
20 /// affects any type variables or unification state.
21 pub struct Match<'a, 'gcx: 'a+'tcx, 'tcx: 'a> {
22 tcx: TyCtxt<'a, 'gcx, 'tcx>
25 impl<'a, 'gcx, 'tcx> Match<'a, 'gcx, 'tcx> {
26 pub fn new(tcx: TyCtxt<'a, 'gcx, 'tcx>) -> Match<'a, 'gcx, 'tcx> {
31 impl<'a, 'gcx, 'tcx> TypeRelation<'a, 'gcx, 'tcx> for Match<'a, 'gcx, 'tcx> {
32 fn tag(&self) -> &'static str { "Match" }
33 fn tcx(&self) -> TyCtxt<'a, 'gcx, 'tcx> { self.tcx }
34 fn a_is_expected(&self) -> bool { true } // irrelevant
36 fn relate_with_variance<T: Relate<'tcx>>(&mut self,
40 -> RelateResult<'tcx, T>
45 fn regions(&mut self, a: ty::Region<'tcx>, b: ty::Region<'tcx>)
46 -> RelateResult<'tcx, ty::Region<'tcx>> {
47 debug!("{}.regions({:?}, {:?})",
54 fn tys(&mut self, a: Ty<'tcx>, b: Ty<'tcx>) -> RelateResult<'tcx, Ty<'tcx>> {
55 debug!("{}.tys({:?}, {:?})", self.tag(),
57 if a == b { return Ok(a); }
59 match (&a.sty, &b.sty) {
60 (_, &ty::Infer(ty::FreshTy(_))) |
61 (_, &ty::Infer(ty::FreshIntTy(_))) |
62 (_, &ty::Infer(ty::FreshFloatTy(_))) => {
67 (_, &ty::Infer(_)) => {
68 Err(TypeError::Sorts(relate::expected_found(self, &a, &b)))
71 (&ty::Error, _) | (_, &ty::Error) => {
72 Ok(self.tcx().types.err)
76 relate::super_relate_tys(self, a, b)
81 fn binders<T>(&mut self, a: &ty::Binder<T>, b: &ty::Binder<T>)
82 -> RelateResult<'tcx, ty::Binder<T>>
85 Ok(ty::Binder::bind(self.relate(a.skip_binder(), b.skip_binder())?))