Errors

Every fallible call returns usearch::Result, whose Error carries a Status and a static message, so nothing allocates on the failure path. A failure the binding catches before the call crosses the boundary reports the status the engine would have used.

match index.on(&executor).search(&rows(&query, 4)?, 10, &mut arena) {
    Ok(matches) => println!("{} queries", matches.queries()),
    Err(Error { status: Status::Contended, .. }) => println!("the arena serves another call"),
    Err(error) => println!("{}: {}", error.status, error.message),
}

Status carries the C enumerators’ values and leaves success to Result, so an Error never carries Status::Deferred, which only Deferred::status reports. Status, Mood, Residency, Traversal, DenseMetric and Scalar print through Display and parse through FromStr the names the C tables own, such as "out-of-memory" or "angular", so nothing is compared as a string. A panic inside a predicate, progress handler or value lookup is caught at the C frame, since unwinding out of one is an abort, and resurfaces once the call is final.