Add Codable support to @published

Published+Codable.swift

import Foundation
import SwiftUI

extension Published:Decodable where Value:Decodable {
    public init(from decoder: Decoder) throws {
        let decoded = try Value(from:decoder)
        self = Published(initialValue:decoded)
    }
}

extension Published:Encodable where Value:Decodable {

    public func encode(to encoder: Encoder) throws {

        let mirror = Mirror(reflecting: self)
        if let valueChild = mirror.children.first(where: { $0.label == "value"
        }) {
            if let value = valueChild.value as? Encodable {
                do {
                    try value.encode(to: encoder)
                    return
                } catch let error {
                    assertionFailure("Failed encoding: \(self) - \(error)")
                }
            }
            else {
                assertionFailure("Decodable Value not decodable. Odd \(self)")
            }
        }
        else {
            assertionFailure("Mirror Mirror on the wall - why no value y'all : \(self)")
        }
    }
}

An approach that is working instead of protocols is using enums:

class Parent {
  @Published var child: Child
}

enum Child: Codable { 
  case custom(_ child: CustomChild)
}

class CustomChild: Codable {
  var value: String
}