Module rustc_infer::infer::relate::combine

There are four type combiners: TypeRelating, Lub, and Glb, and NllTypeRelating in rustc_borrowck, which is only used for NLL.

Each implements the trait TypeRelation and contains methods for combining two instances of various things and yielding a new instance. These combiner methods always yield a Result<T>. To relate two types, you can use infcx.at(cause, param_env) which then allows you to use the relevant methods of At.

Combiners mostly do their specific behavior and then hand off the bulk of the work to InferCtxt::super_combine_tys and InferCtxt::super_combine_consts.

Combining two types may have side-effects on the inference contexts which can be undone by using snapshots. You probably want to use either InferCtxt::commit_if_ok or InferCtxt::probe.

On success, the LUB/GLB operations return the appropriate bound. The return value of Equate or Sub shouldn’t really be used.

Structs

• CombineFields

Enums

• VarianceDiagInfo
  Extra information about why we ended up with a particular variance. This is only used to add more information to error messages, and has no effect on soundness. While choosing the ‘wrong’ VarianceDiagInfo may lead to confusing notes in error messages, it will never cause a miscompilation or unsoundness.

Traits

• PredicateEmittingRelation
• Relate
• TypeRelation

Functions

• relate_args_invariantly
• relate_args_with_variances
• structurally_relate_consts
  Relates a and b structurally, calling the relation for all nested values. Any semantic equality, e.g. of unevaluated consts, and inference variables have to be handled by the caller.
• structurally_relate_tys
  Relates a and b structurally, calling the relation for all nested values. Any semantic equality, e.g. of projections, and inference variables have to be handled by the caller.