Filtered Search

The predicate runs on the executor’s threads, so it must be @Sendable and safe for concurrent use; an error it throws rejects that key. Non-matching entries still route the traversal, so recall does not collapse at low selectivity. DenseSearchConfig(traversal: .scan) skips the walk and scores every entry exactly, on RAM and NVMe handles, the fallback for a filter too selective for a walk to cross.

let even = try index.on(executor).search(queries, wanted: 10, arena: arena, config: DenseSearchConfig(
    predicate: { key in key.integerIdentity.map { $0 % 2 == 0 } ?? false }))

Every long verb’s config, and every lifecycle config that reports, takes a progress handler, called with the units finished so far and the units the call finishes if it runs to the end; returning .cancel stops it with cancelled wherever the verb can stop, which an insert cannot. A handler never runs on two threads at once, so it may carry a counter or a deadline without a lock, but it may run on whichever thread advanced the work, hence @Sendable. A predicate, handler or value lookup that throws never unwinds into C; the first error stops the call where it can and is thrown once the call is final, a USearchError as it was and any other as the cause of a cancelled one.

let deadline = ContinuousClock.now + .seconds(30)
try index.on(executor).refine(config: DenseRefineConfig(
    expansionFactor: 128,
    progress: { _, _ in ContinuousClock.now < deadline ? .continue : .cancel }))