1 use crate::ty::error::TypeError;
2 use crate::ty::relate::{self, Relate, RelateResult, TypeRelation};
3 use crate::ty::{self, InferConst, Ty, TyCtxt};
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 {
36 fn tcx(&self) -> TyCtxt<'tcx> {
39 fn param_env(&self) -> ty::ParamEnv<'tcx> {
42 fn a_is_expected(&self) -> bool {
46 fn relate_with_variance<T: Relate<'tcx>>(
51 ) -> RelateResult<'tcx, T> {
59 ) -> RelateResult<'tcx, ty::Region<'tcx>> {
60 debug!("{}.regions({:?}, {:?})", self.tag(), a, b);
64 fn tys(&mut self, a: Ty<'tcx>, b: Ty<'tcx>) -> RelateResult<'tcx, Ty<'tcx>> {
65 debug!("{}.tys({:?}, {:?})", self.tag(), a, b);
70 match (a.kind(), b.kind()) {
73 &ty::Infer(ty::FreshTy(_))
74 | &ty::Infer(ty::FreshIntTy(_))
75 | &ty::Infer(ty::FreshFloatTy(_)),
78 (&ty::Infer(_), _) | (_, &ty::Infer(_)) => {
79 Err(TypeError::Sorts(relate::expected_found(self, &a, &b)))
82 (&ty::Error(_), _) | (_, &ty::Error(_)) => Ok(self.tcx().ty_error()),
84 _ => relate::super_relate_tys(self, a, b),
90 a: &'tcx ty::Const<'tcx>,
91 b: &'tcx ty::Const<'tcx>,
92 ) -> RelateResult<'tcx, &'tcx ty::Const<'tcx>> {
93 debug!("{}.consts({:?}, {:?})", self.tag(), a, b);
98 match (a.val, b.val) {
99 (_, ty::ConstKind::Infer(InferConst::Fresh(_))) => {
103 (ty::ConstKind::Infer(_), _) | (_, ty::ConstKind::Infer(_)) => {
104 return Err(TypeError::ConstMismatch(relate::expected_found(self, &a, &b)));
110 relate::super_relate_consts(self, a, b)
117 ) -> RelateResult<'tcx, ty::Binder<T>>
121 Ok(a.rebind(self.relate(a.skip_binder(), b.skip_binder())?))