1 use crate::ty::{self, Ty, TyCtxt, InferConst};
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<'tcx> {
23 param_env: ty::ParamEnv<'tcx>,
27 pub fn new(tcx: TyCtxt<'tcx>, param_env: ty::ParamEnv<'tcx>) -> Match<'tcx> {
28 Match { tcx, param_env }
32 impl TypeRelation<'tcx> for Match<'tcx> {
33 fn tag(&self) -> &'static str { "Match" }
34 fn tcx(&self) -> TyCtxt<'tcx> { self.tcx }
35 fn param_env(&self) -> ty::ParamEnv<'tcx> { self.param_env }
36 fn a_is_expected(&self) -> bool { true } // irrelevant
38 fn relate_with_variance<T: Relate<'tcx>>(&mut self,
42 -> RelateResult<'tcx, T>
47 fn regions(&mut self, a: ty::Region<'tcx>, b: ty::Region<'tcx>)
48 -> RelateResult<'tcx, ty::Region<'tcx>> {
49 debug!("{}.regions({:?}, {:?})",
56 fn tys(&mut self, a: Ty<'tcx>, b: Ty<'tcx>) -> RelateResult<'tcx, Ty<'tcx>> {
57 debug!("{}.tys({:?}, {:?})", self.tag(),
59 if a == b { return Ok(a); }
61 match (&a.kind, &b.kind) {
62 (_, &ty::Infer(ty::FreshTy(_))) |
63 (_, &ty::Infer(ty::FreshIntTy(_))) |
64 (_, &ty::Infer(ty::FreshFloatTy(_))) => {
69 (_, &ty::Infer(_)) => {
70 Err(TypeError::Sorts(relate::expected_found(self, &a, &b)))
73 (&ty::Error, _) | (_, &ty::Error) => {
74 Ok(self.tcx().types.err)
78 relate::super_relate_tys(self, a, b)
85 a: &'tcx ty::Const<'tcx>,
86 b: &'tcx ty::Const<'tcx>,
87 ) -> RelateResult<'tcx, &'tcx ty::Const<'tcx>> {
88 debug!("{}.consts({:?}, {:?})", self.tag(), a, b);
93 match (a.val, b.val) {
94 (_, ty::ConstKind::Infer(InferConst::Fresh(_))) => {
98 (ty::ConstKind::Infer(_), _) | (_, ty::ConstKind::Infer(_)) => {
99 return Err(TypeError::ConstMismatch(relate::expected_found(self, &a, &b)));
105 relate::super_relate_consts(self, a, b)
108 fn binders<T>(&mut self, a: &ty::Binder<T>, b: &ty::Binder<T>)
109 -> RelateResult<'tcx, ty::Binder<T>>
110 where T: Relate<'tcx>
112 Ok(ty::Binder::bind(self.relate(a.skip_binder(), b.skip_binder())?))