pub struct TypeTest<'tcx> {
    pub generic_kind: GenericKind<'tcx>,
    pub lower_bound: RegionVid,
    pub locations: Locations,
    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.

locations: Locations

Where did this constraint arise and why?

verify_bound: VerifyBound<'tcx>

A test which, if met by the region 'x, proves that this type constraint is satisfied.

Trait Implementations

Returns a copy of the value. Read more
Performs copy-assignment from source. Read more
Formats the value using the given formatter. Read more

Auto Trait Implementations

Blanket Implementations

Gets the TypeId of self. Read more
Immutably borrows from an owned value. Read more
Mutably borrows from an owned value. Read more

Returns the argument unchanged.

Calls U::from(self).

That is, this conversion is whatever the implementation of From<T> for U chooses to do.

The resulting type after obtaining ownership.
Creates owned data from borrowed data, usually by cloning. Read more
Uses borrowed data to replace owned data, usually by cloning. Read more
The type returned in the event of a conversion error.
Performs the conversion.
The type returned in the event of a conversion error.
Performs the conversion.

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