Published like SwiftUI

Published.swift

//
//  ViewController.swift
//  Teeeeee
//
//  Created by Bartleby Cartman on 23.11.2020.
//

import UIKit

class ViewController: UIViewController, UITextFieldDelegate {
    @IBOutlet var textField: UITextField!
    @IBOutlet var textLabel: UILabel!
    
    @Published var stringValue: String = ""
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        textLabel << $stringValue
        
        // Do any additional setup after loading the view.
    }

    func textFieldDidChangeSelection(_ textField: UITextField) {
        stringValue = textField.text ?? ""
    }
}


// MARK: - Property Wrapper
@propertyWrapper
struct Published<Value> {
    var wrappedValue: Value {
        get { subject.value }
        set { subject.value = newValue }
    }
    
    private let subject: CurrentValueSubject<Value, Never>
    
    var projectedValue: CurrentValueSubject<Value, Never> { subject }
    
    init(wrappedValue: Value) {
        self.subject = CurrentValueSubject(wrappedValue)
    }
}

// MARK: - Subject
final class CurrentValueSubject<Output, Failure: Error> {
    typealias Reciver = (Output) -> Bool
    var recivers: [Reciver] = []
    private let lock = NSRecursiveLock()
    
    private var currentValue: Output
    
    var value: Output {
        set {
            lock.lock()
            sendValueAndConsumeLock(newValue)
        }
        
        get {
            return currentValue
        }
    }
    
    init(_ value: Output) {
        self.currentValue = value
    }
    
    func sink(_ context: AnyObject, receiveValue: @escaping (Output) -> Void) {
        lock.lock()
        defer { lock.unlock() }
        
        self.recivers.append({ [weak context] v in
            guard context != nil else { return false }
            receiveValue(v)
            return true
        })
    }
    
    private func sendValueAndConsumeLock(_ newValue: Output) {
        defer { lock.unlock() }
        currentValue = newValue
        self.recivers = self.recivers.filter { $0(newValue) }
    }
}

// MARK: - UILabel extension
extension UILabel: Bindable {
    func bind<V>(_ b: CurrentValueSubject<V, Never>) {
        b.sink(self) { (value) in
            self.text = String(describing: value)
        }
    }
}

// MARK: - Bindable Protocol
protocol Bindable {
    func bind<V>(_ b: CurrentValueSubject<V, Never>)
}

// MARK: - Custom Operator
infix operator <<
func <<<T, V>(lhs: T, rhs: CurrentValueSubject<V, Never>) where T: Bindable {
    lhs.bind(rhs)
}