A conditional debounce operator.

ClearingDebounceTests.swift

class Tests: XCTestCase {
    var scheduler: TestScheduler!
    var result: TestableObserver<String>!
    var disposeBag: DisposeBag!

    override func setUp() {
        super.setUp()
        scheduler = TestScheduler(initialClock: 0, resolution: 0.1)
        result = scheduler.createObserver(String.self)
        disposeBag = DisposeBag()
    }

    func test1() {
        let source = scheduler.createColdObservable([.next(0, ""), .next(10, "H"), .next(20, "He"), .next(40, "Hel")])
        source
            .clearingDebounce(isDebounced: { !$0.isEmpty }, delay: .seconds(1), scheduler: scheduler)
            .subscribe(result)
            .disposed(by: disposeBag)

        scheduler.start()

        XCTAssertEqual(result.events, [.next(0, ""), .next(30, "He"), .next(50, "Hel")])
    }

    func test2() {
        let source = scheduler.createColdObservable([.next(0, ""), .next(10, "H"), .next(30, "He"), .next(40, "")])
        source
            .clearingDebounce(isDebounced: { !$0.isEmpty }, delay: .seconds(1), scheduler: scheduler)
            .subscribe(result)
            .disposed(by: disposeBag)

        scheduler.start()

        XCTAssertEqual(result.events, [.next(0, ""), .next(20, "H"), .next(40, "")])
    }
}

ClearningDebounce.swift

//
//  ClearningDebounce.swift
//
//  Created by Daniel Tartaglia on 21 Aug 2019.
//  Copyright © 2019 Daniel Tartaglia. MIT License.
//

import RxSwift

extension ObservableType {
    func clearingDebounce(isDebounced: @escaping (Element) -> Bool, delay: RxTimeInterval, scheduler: SchedulerType) -> Observable<Element> {
        flatMapLatest {
            isDebounced($0) ? Observable.just($0).delay(delay, scheduler: scheduler) : Observable.just($0)
        }
    }
}