rx swift texfield validation and scanning

UITextFieldReactiveExtension.swift

extension Reactive where Base: UITextField {
    
    public func validateWithRegex(value:String) -> ControlProperty<String?> {
        let original: ControlProperty<String?> = self.text
        
        let values: Observable<String?> = original.map { self.validate(text: $0, regex: value) }
        let valueSink: AnyObserver<String?> = original.mapObserver { $0 }
        return ControlProperty<String?>(values: values, valueSink: valueSink)
    }
    
    public func scanWithRegExp(value:String) -> ControlProperty<String> {
        let original: ControlProperty<String> = self.text.orEmpty
        
        
        let values: Observable<String> = original.scan("", accumulator: self.shouldChangeText(regex: value))
            .do(onNext: { self.base.text = $0})
        let valueSink: AnyObserver<String> = original.mapObserver { $0 }
        return ControlProperty<String>(values: values, valueSink: valueSink)
    }
    
    
    private func shouldChangeText(regex:String) -> ((String,String) -> String){
        return { (prev,next) in
            
            if next.count == 0{
                return next
            }
            
            if (next ~= regex) == false{
                return prev
            }
            
            return next
        }
    }
    
    private func validate(text:String?, regex:String) -> String?{
        
   
        
        guard let text = text else{
            return nil
        }
        if text.isEmpty == true{
            return text
        }
        
        return (text ~= regex) ? text : nil
        
    }
    
}