NSKeyedUnarchiver creates multiple instances of the same object references by others

Question

I'm experimenting with NSKeyedArchiver because I'm looking into saving an object graph. However, there seems to be a problem with objects referencing the same instance of another object. Say, I have three classes: A, B and C that reference each other like this:

A --> B <-- C

A and C each have a reference to the same object B. When decoding this using NSKeyedUnarchiver, it simply creates multiple instances of B so that A and B do not reference the same object anymore.

Here's a full example:

import Foundation

class A: Codable {
    var b: B
    
    init(b: B) {
        self.b = b
    }
    
    required init(from decoder: Decoder) throws {
        let container = try decoder.container(keyedBy: CodingKeys.self)
        self.b = try container.decode(B.self, forKey: .b)
    }
    
    func encode(to encoder: Encoder) throws {
        var container = encoder.container(keyedBy: CodingKeys.self)
        try container.encode(b, forKey: .b)
    }
    
    private enum CodingKeys: String, CodingKey {
        case b
    }
}

class B: Codable {
    init() {}
    required init(from decoder: Decoder) throws {}
    func encode(to encoder: Encoder) throws {}
}

class C: Codable {
    var b: B
    
    init(b: B) {
        self.b = b
    }
    
    required init(from decoder: Decoder) throws {
        let container = try decoder.container(keyedBy: CodingKeys.self)
        self.b = try container.decode(B.self, forKey: .b)
    }
    
    func encode(to encoder: Encoder) throws {
        var container = encoder.container(keyedBy: CodingKeys.self)
        try container.encode(b, forKey: .b)
    }
    
    private enum CodingKeys: String, CodingKey {
        case b
    }
}

class Store: Codable {
    var a: A
    var b: B
    var c: C
    
    init() {
        b = B()
        a = A(b: b)
        c = C(b: b)
    }
    
    required init(from decoder: Decoder) throws {
        let container = try decoder.container(keyedBy: CodingKeys.self)
        self.a = try container.decode(A.self, forKey: .a)
        self.b = try container.decode(B.self, forKey: .b)
        self.c = try container.decode(C.self, forKey: .c)
    }
    
    func encode(to encoder: Encoder) throws {
        var container = encoder.container(keyedBy: CodingKeys.self)
        try container.encode(a, forKey: .a)
        try container.encode(b, forKey: .b)
        try container.encode(c, forKey: .c)
    }
    
    private enum CodingKeys: String, CodingKey {
        case a, b, c
    }
}

let store = Store()

let archiver = NSKeyedArchiver(requiringSecureCoding: false)
try! archiver.encodeEncodable(store, forKey: NSKeyedArchiveRootObjectKey)
archiver.finishEncoding()

let unarchiver = try! NSKeyedUnarchiver(forReadingFrom: archiver.encodedData)
if let decodedStore = try! unarchiver.decodeTopLevelDecodable(Store.self, forKey: NSKeyedArchiveRootObjectKey) {
    // Will print false
    print(decodedStore.a.b === decodedStore.c.b)
}

Am I doing something wrong or does something like this simply not work? Or is my example flawed?

Thanks!