Hack Codable support on to @published (don't use this 😅)

Published+Codable.swift

extension Published: Decodable where Value: Decodable {
    public init(from decoder: Decoder) throws {
        try self.init(initialValue: Value(from: decoder))
    }
}
extension Published: Encodable where Value: Encodable {
    public func encode(to encoder: Encoder) throws {
        let mirror = Mirror(reflecting: self)

        // The internal structure uses a `Storage` enum
        // The case that is used appears to depend on how the instance is being used
        func value() -> Value? {
            return mirror.descendant("storage", "value") as? Value
        }
        func publisherValue() -> Value? {
            return mirror.descendant("storage", "publisher", "subject", "currentValue") as? Value
        }

        guard let value = value() ?? publisherValue() else {
            throw EncodingError.invalidValue(self, .init(codingPath: encoder.codingPath, debugDescription: "Unable to find value"))
        }

        try value.encode(to: encoder)
    }
}

xample.swift

class State: ObservableObject, Codable {
    @Published var foo: Int = 0
    @Published var bar: String = "hello world"
}

let state = State()
state.foo = 42
let data = try! JSONEncoder().encode(state)

print(String(data: data, encoding: .utf8)!) // {"foo":42,"bar":"hello world"}

let model = try! JSONDecoder().decode(State.self, from: data)
print(model.foo) // 42
print(model.bar) // hello world