Binding in Swift

Box.swift

import UIKit

class Box<T> {
    typealias Listener = (T) -> Void
    private var listener: Listener?
    private var dispatchThread: DispatchQueue = DispatchQueue.main

    var value: T {
        didSet {
            dispatchThread.async { [weak self] in
                guard let `self` = self else { return }

                self.listener?(self.value)
            }
        }
    }

    init(_ v: T) {
        value = v
    }

    init(value: T, dispatchThread: DispatchQueue) {
        self.value = value
        self.dispatchThread = dispatchThread
    }
}

extension Box {

    func bind(listener: Listener?) {
        self.listener = listener
    }

    func bindAndFire(listener: Listener?) {
        self.listener = listener
        listener?(value)
    }
}

extension Box where T == String {

    func bind(to label: UITextField) {
        weak var weakInstance = label
        self.listener = { (value) in
            weakInstance?.text = value
        }
    }

    func bindAndFire(to label: UITextField) {
        self.bind(to: label)
        listener?(value)
    }

    func bind(to button: UIButton) {
        weak var weakInstance = button
        self.listener = { (value) in
            weakInstance?.setTitle(value, for: .normal)
        }
    }

    func bindAndFire(to button: UIButton) {
        self.bind(to: button)
        listener?(value)
    }

    func bind(to imageView: UIImageView) {
        weak var weakInstance = imageView
        self.listener = { (value) in
            weakInstance?.image = UIImage(named: value)
        }
    }

    func bindAndFire(to imageView: UIImageView) {
        self.bind(to: imageView)
        listener?(value)
    }
}