Struct rustc_middle::ty::_match::MatchAgainstFreshVars

pub struct MatchAgainstFreshVars<'tcx> {
    tcx: TyCtxt<'tcx>,
}

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.

Fields

tcx: TyCtxt<'tcx>

Implementations

impl<'tcx> MatchAgainstFreshVars<'tcx>

pub fn new(tcx: TyCtxt<'tcx>) -> MatchAgainstFreshVars<'tcx>

Trait Implementations

impl<'tcx> TypeRelation<'tcx> for MatchAgainstFreshVars<'tcx>

fn tag(&self) -> &'static str

Returns a static string we can use for printouts.

fn tcx(&self) -> TyCtxt<'tcx>

fn a_is_expected(&self) -> bool

Returns true if the value a is the “expected” type in the relation. Just affects error messages.

fn relate_with_variance<T: Relate<'tcx>>( &mut self, _: Variance, _: VarianceDiagInfo<'tcx>, a: T, b: T ) -> RelateResult<'tcx, T>

Switch variance for the purpose of relating a and b.

fn regions( &mut self, a: Region<'tcx>, b: Region<'tcx> ) -> RelateResult<'tcx, Region<'tcx>>

fn tys(&mut self, a: Ty<'tcx>, b: Ty<'tcx>) -> RelateResult<'tcx, Ty<'tcx>>

fn consts( &mut self, a: Const<'tcx>, b: Const<'tcx> ) -> RelateResult<'tcx, Const<'tcx>>

fn binders<T>( &mut self, a: Binder<'tcx, T>, b: Binder<'tcx, T> ) -> RelateResult<'tcx, Binder<'tcx, T>>

where T: Relate<'tcx>,

fn with_cause<F, R>(&mut self, _cause: Cause, f: F) -> R

where F: FnOnce(&mut Self) -> R,

fn relate<T: Relate<'tcx>>(&mut self, a: T, b: T) -> RelateResult<'tcx, T>

Generic relation routine suitable for most anything.

fn relate_item_args( &mut self, item_def_id: DefId, a_arg: GenericArgsRef<'tcx>, b_arg: GenericArgsRef<'tcx> ) -> RelateResult<'tcx, GenericArgsRef<'tcx>>

Relate the two args for the given item. The default is to look up the variance for the item and proceed accordingly.

Layout

Note: Most layout information is completely unstable and may even differ between compilations. The only exception is types with certain repr(...) attributes. Please see the Rust Reference's “Type Layout” chapter for details on type layout guarantees.

Size: 8 bytes