Refinement with multi-field predicates

Area: Refinement & types Teaches: a refinement predicate is an ordinary boolean expression — it can read several fields and combine them with &&/||, comparisons, and string equality. Prerequisites: refinement (iff/where). Run: ox build examples/multi_field_refinement && ox run-scenario examples/multi_field_refinement

A single iff refinement classifies a Person by two fields at once:

pub type ActiveAdult <: Person iff {
    self.age >= 18 && self.status == "active"
};

ActiveAdult is the subset of people who are both adults and active. The predicate is evaluated per individual at query time against that individual’s declared fields — no membership is stored.

Running it

The scenario registers four people; only those satisfying both conjuncts are classified:

alice  age=25  status="active"    → ActiveAdult
bob    age=12  status="active"    → not (fails age >= 18)
carol  age=30  status="inactive"  → not (fails status == "active")
dave   age=45  status="active"    → ActiveAdult

so active_adults returns 2 rows (alice, dave) out of the 4 in all_people.

This example is compiled and run in CI; its runtime behaviour is pinned by a corpus test (oxc-runtime/tests/examples_corpus.rs).