包含数组元素的数组的深度副本?

我正在尝试对以下对象的列表进行深度复制:

struct Book {
    var title: String
    var author: String
    var pages: Int
}

struct BookShelf {
    var number: Int
}

class BookShelfViewModel {
    var bookShelf: BookShelf

    var number: Int
    var books: [BookViewModel]?

    init(bookShelf: BookShelf) {
        self.bookShelf = bookShelf

        self.number = bookShelf.number
    }

    required init(original: BookShelfViewModel) {
        self.bookShelf = original.bookShelf

        self.number = original.number
    }
}

class BookViewModel {
    var book: Book

    var title: String
    var author: String
    var pages: Int

    init(book: Book) {
        self.book = book

        self.title = book.title
        self.author = book.author
        self.pages = book.pages
    }

    required init(original: BookViewModel) {
        self.book = original.book

        self.title = original.title
        self.author = original.author
        self.pages = original.pages
    }
}

书架上的书在书架模型里取。

如果我喜欢:

var copiedArray = originalArray

for bs in copiedArray {
   bs.books = bs.books.filter { $0.title == "SampleTitle" }
}

当我像这样克隆阵列时:

var originalArray = [BookShelfViewModel]()
... // Fill the array
var clonedArray = originalArray.clone()

克隆了clonedArray,但clonedArray.books为空。

我已经创建了扩展并遵循 this 主旨。如何在数组中的对象中克隆数组?

我做了一个简单的练习来形象化这个问题,希望它能帮助理解我在说什么。