RxSwift SubscribeIf

TFObservable.swift

import UIKit
import RxSwift

class TFObservable<E> {
    var disposable: Disposable
    
    private var trueBlock: ((E) -> Void)?
    private var falseBlock: ((E) -> Void)?
    
    init() {
        self.trueBlock = nil
        self.falseBlock = nil
        self.disposable = Observable.just(false).subscribe()
    }
    
    func onTrue(element: E) {
        if let block = trueBlock {
            block(element)
        }
    }
    
    func onFalse(element: E) {
        if let block = falseBlock {
            block(element)
        }
    }
    
    func `true`(_ block: @escaping (E) -> Void) -> TFObservable {
        self.trueBlock = block
        return self
    }
    
    func `false`(_ block: @escaping (E) -> Void) -> Disposable {
        self.falseBlock = block
        return disposable
    }
    
    func disposed(by bag: DisposeBag) {
        disposable
            .disposed(by: bag)
    }
}

extension Observable {
    func subscribeIf(_ block: @escaping (Element) -> Bool) -> TFObservable<Element> {
        let tf = TFObservable<Element>()
        tf.disposable = subscribe(onNext: { (element) in
            block(element) ? tf.onTrue(element: element) : tf.onFalse(element: element)
        })
        return tf
    }
}

class ViewController: UIViewController {
    var subject = PublishSubject<String>()
    var otherSubject = PublishSubject<Int>()
    
    var disposeBag = DisposeBag()
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        subject
            .subscribeIf { (value) -> Bool in
                return value == "Hello World"
            }
            
            .true { (value) in
                print("True: \(value)")
            }
            
            .false { (value) in
                print("False: \(value)")
            }
            
            .disposed(by: disposeBag)
        
        
        
        otherSubject
            .subscribeIf { $0 == 5423 }
            .true { print("value: \($0) == 5423") }
            .disposed(by: disposeBag)
        
        
        // On Next
        
        otherSubject.onNext(123)
        otherSubject.onNext(5423)
        
        subject.onNext("Hello")
        subject.onNext("Hello World")
    }
}