Struct rustc_mir::borrow_check::nll::region_infer::TypeTest [−][src]
pub struct TypeTest<'tcx> { pub generic_kind: GenericKind<'tcx>, pub lower_bound: RegionVid, pub locations: Locations, pub test: RegionTest, }
🔬 This is a nightly-only experimental API. (rustc_private
)
this crate is being loaded from the sysroot, an unstable location; did you mean to load this crate from crates.io via Cargo.toml
instead?
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::outlives
.
Fields
generic_kind: GenericKind<'tcx>
🔬 This is a nightly-only experimental API. (rustc_private
)
this crate is being loaded from the sysroot, an unstable location; did you mean to load this crate from crates.io via Cargo.toml
instead?
The type T
that must outlive the region.
lower_bound: RegionVid
🔬 This is a nightly-only experimental API. (rustc_private
)
this crate is being loaded from the sysroot, an unstable location; did you mean to load this crate from crates.io via Cargo.toml
instead?
The region 'x
that the type must outlive.
locations: Locations
🔬 This is a nightly-only experimental API. (rustc_private
)
this crate is being loaded from the sysroot, an unstable location; did you mean to load this crate from crates.io via Cargo.toml
instead?
Where did this constraint arise and why?
test: RegionTest
🔬 This is a nightly-only experimental API. (rustc_private
)
this crate is being loaded from the sysroot, an unstable location; did you mean to load this crate from crates.io via Cargo.toml
instead?
A test which, if met by the region 'x
, proves that this type
constraint is satisfied.
Trait Implementations
impl<'tcx> Clone for TypeTest<'tcx>
[src]
impl<'tcx> Clone for TypeTest<'tcx>
fn clone(&self) -> TypeTest<'tcx>
[src]
fn clone(&self) -> TypeTest<'tcx>
Returns a copy of the value. Read more
fn clone_from(&mut self, source: &Self)
1.0.0[src]
fn clone_from(&mut self, source: &Self)
Performs copy-assignment from source
. Read more
impl<'tcx> Debug for TypeTest<'tcx>
[src]
impl<'tcx> Debug for TypeTest<'tcx>