通用类

Question

我正在尝试以通用方式实现项目的特定部分，但是我正在努力进行类型检查。模型有两种类型-Service和Product（1-N关系）。在下面的代码中，Service被视为节，而Product被视为节项目。

protocol ItemSectionable: class {

    associatedtype SectionItemType

    func getSection() -> Int
    func getSectionName() -> String
    func getItem(index: Int) -> SectionItemType
}


class Service: Object, Model, ItemSectionable {

    typealias ModelType = Service
    typealias SectionItemType = Product

    @objc dynamic var id: Int = 0
    @objc dynamic var name: String = ""
    @objc dynamic var enabled: Bool = false

    @objc dynamic var deleted: Bool = false
    @objc dynamic var createdAt = Date()
    @objc dynamic var updatedAt = Date()

    let products = List<Product>()

    override static func primaryKey() -> String? {
        return "id"
    }

    static func newInstance(values: Object) -> Service {
        let _service = values as! Service

        let service = Service(value: _service)
        _service.products.forEach { _product in
            service.products.append(Product(value: _product))
        }

        return service
    }

    func getSection() -> Int {
        return products.count
    }

    func getSectionName() -> String {
        return name
    }

    func getItem(index: Int) -> Product {
        return products[index]
    }
}

class Product: Object, Model {

    typealias ModelType = Product

    @objc dynamic var id: Int = 0
    @objc dynamic var name: String = ""
    @objc dynamic var code: String = ""
    @objc dynamic var salesPrice: Float = 0

    @objc dynamic var deleted: Bool = false
    @objc dynamic var createdAt = Date()
    @objc dynamic var updatedAt = Date()

    let service = LinkingObjects(fromType: Service.self, property: "products")

    override static func primaryKey() -> String? {
        return "id"
    }

    static func newInstance(values: Object) -> Product {
        let product = Product(value: values)
        return product
    }
}

此外，我有一个通用的RealmListSectionModelManager，它扩展了RealmListModelManager的大部分功能，并实现了将数据拆分为多个部分的支持。

class RealmListSectionModelManager<T: Model & ItemSectionable>: RealmListModelManager<T> where T: Object {

    // Get number of sections
    override func getSectionCount() -> Int {
        return data?.count ?? 1
    }

    // Get number of items in a section
    override func getSectionItemCount(section: Int = 0) -> Int {
        return data?[section].getSection() ?? 0
    }

    // Get item for a specific section
    override func getItem(index: Int, section: Int) -> ItemSectionable.SectionItemType <-- No idea how to write this correctly {
        return data![section].getItem(index: index)
    }
}

我遇到的问题是关于getItem(index: Int, section: Int)中的RealmListSectionModelManager函数，该函数应返回基于ItemSectionable's associatedtype（SectionItemType）的类型，但是我不知道如何正确地做到这一点。