RxCaptureMetadataOutputObjectsDelegateProxy and Reactive extension to (_:didOutput:from:) method

RxCaptureMetadataOutputObjectsDelegateProxy.swift

import Foundation
import AVFoundation
import RxSwift
import RxCocoa

class RxCaptureMetadataOutputObjectsDelegateProxy: 
    DelegateProxy<AVCaptureMetadataOutput, AVCaptureMetadataOutputObjectsDelegate>, 
    DelegateProxyType,  
    AVCaptureMetadataOutputObjectsDelegate {
    
    private(set) var metadataOutput: AVCaptureMetadataOutput?
    
    public init(metadataOutput: AVCaptureMetadataOutput) {
        self.metadataOutput = metadataOutput
        super.init(parentObject: metadataOutput, 
                   delegateProxy: RxCaptureMetadataOutputObjectsDelegateProxy.self)
    }
  
    static func registerKnownImplementations() {
        self.register { RxCaptureMetadataOutputObjectsDelegateProxy(metadataOutput: $0) }
    }
    
    static func currentDelegate(for object: AVCaptureMetadataOutput) -> AVCaptureMetadataOutputObjectsDelegate? {
        return object.metadataObjectsDelegate
    }
    
    static func setCurrentDelegate(_ delegate: AVCaptureMetadataOutputObjectsDelegate?, to object: AVCaptureMetadataOutput) {
        object.setMetadataObjectsDelegate(delegate.map { $0 }, 
                                          queue: DispatchQueue.main)
    }
    
}

extension Reactive where Base: AVCaptureMetadataOutput {
    
    public var delegate: DelegateProxy<AVCaptureMetadataOutput, AVCaptureMetadataOutputObjectsDelegate> {
        return RxCaptureMetadataOutputObjectsDelegateProxy
            .proxy(for: base)
    }
    
    public var didOutputMetadataObjects: Observable<([AnyObject], AVCaptureConnection)> {
        return delegate
            .methodInvoked(#selector(AVCaptureMetadataOutputObjectsDelegate.metadataOutput(_:didOutput:from:)))
            .map { ($0[1] as! [AnyObject], $0[2] as! AVCaptureConnection) }
    }
}