Struct rustc_borrowck::region_infer::TypeTest
source · pub struct TypeTest<'tcx> {
pub generic_kind: GenericKind<'tcx>,
pub lower_bound: RegionVid,
pub span: Span,
pub verify_bound: VerifyBound<'tcx>,
}
Expand description
A “type test” corresponds to an outlives constraint between a type
and a lifetime, like T: 'x
or <T as Foo>::Bar: 'x
. They are
translated from the Verify
region constraints in the ordinary
inference context.
These sorts of constraints are handled differently than ordinary
constraints, at least at present. During type checking, the
InferCtxt::process_registered_region_obligations
method will
attempt to convert a type test like T: 'x
into an ordinary
outlives constraint when possible (for example, &'a T: 'b
will
be converted into 'a: 'b
and registered as a Constraint
).
In some cases, however, there are outlives relationships that are not converted into a region constraint, but rather into one of these “type tests”. The distinction is that a type test does not influence the inference result, but instead just examines the values that we ultimately inferred for each region variable and checks that they meet certain extra criteria. If not, an error can be issued.
One reason for this is that these type tests typically boil down
to a check like 'a: 'x
where 'a
is a universally quantified
region – and therefore not one whose value is really meant to be
inferred, precisely (this is not always the case: one can have a
type test like <Foo as Trait<'?0>>::Bar: 'x
, where '?0
is an
inference variable). Another reason is that these type tests can
involve disjunction – that is, they can be satisfied in more
than one way.
For more information about this translation, see
InferCtxt::process_registered_region_obligations
and
InferCtxt::type_must_outlive
in rustc_infer::infer::InferCtxt
.
Fields§
§generic_kind: GenericKind<'tcx>
The type T
that must outlive the region.
lower_bound: RegionVid
The region 'x
that the type must outlive.
span: Span
The span to blame.
verify_bound: VerifyBound<'tcx>
A test which, if met by the region 'x
, proves that this type
constraint is satisfied.
Trait Implementations§
Auto Trait Implementations§
impl<'tcx> !RefUnwindSafe for TypeTest<'tcx>
impl<'tcx> !Send for TypeTest<'tcx>
impl<'tcx> !Sync for TypeTest<'tcx>
impl<'tcx> Unpin for TypeTest<'tcx>
impl<'tcx> !UnwindSafe for TypeTest<'tcx>
Blanket Implementations§
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: 72 bytes