ios – 如何通过Swift中的泛型类型构造一个属性？

class Sample<ItemType,AdaptorType> {
    var items = Array<ItemType>() 
    let adaptor = AdaptorType()   //Error: 'AdaptorType' is not constructible with '()'
}

我也尝试在init()中初始化它,但是同样的问题在于

class SampleGnericclass<ItemType,AdaptorType> {
    var items = Array<ItemType>() 
    let adaptor : AdaptorType

    init() {
        adaptor = AdaptorType()      //It doesn't work,same error occors here
    }
}

使用通用类型AdaptorType初始化适配器属性的正确方法是什么？万分感谢！

编辑：关于这个问题的完整代码

import UIKit

protocol XYManagedobject {

}

protocol XYNetworkProtocol {

    typealias ManagedobjectType : XYManagedobject

    func object(fromItemDictionary dictionary: NSDictionary?) -> ManagedobjectType?
    func objects(fromEntryDictionary dictionary: NSDictionary?) -> Array<ManagedobjectType>?
    func actionParameters(page: UInt?) -> (action: String,parameters: Dictionary<String,String>?)
    func pageSize() -> UInt? // nil for unlimited
}

class ProductAdaptor : XYNetworkProtocol {

    var filter = Dictionary<String,String>()

    typealias ManagedobjectType = XYProductObject

    func object(fromItemDictionary dictionary: NSDictionary?) -> ManagedobjectType? {
        //... Will return an object here
        return nil
    }

    func objects(fromEntryDictionary dictionary: NSDictionary?) -> Array<ManagedobjectType>? {
        //... will return an array of objects here
        return nil
    }

    func actionParameters(page: UInt?) -> (action: String,String>?) {
        var parameters = filter
        if page {
            parameters["page"] = "\(page!)"
        }

        return ("product_list",parameters)
    }

    func pageSize() -> UInt? {
        return 100
    }
}

class XYDataManager<ItemType: XYManagedobject,AdaptorType: XYNetworkProtocol> {

    var objects = Array<ItemType>()
    let adaptor = ProductAdaptor() //work around,adaptor should be any type conform to XYNetworkProtocol

    func loadPage(page: UInt?) -> (hasNextPage: Bool,items: Array<ItemType>?) {
        let fetcher = XYFetchController()

        let ap = adaptor.actionParameters(page)
        if let fetchedResult = fetcher.JSONObjectForAPI(ap.action,parameters: ap.parameters) {

            let npage = fetchedResult["npage"].integerValue
            var hasNextPage = true
            if !npage || !page {
                hasNextPage = false
            }
            else if npage <= page {
                hasNextPage = false
            }

            let objects = adaptor.objects(fromEntryDictionary: fetchedResult)
            return (hasNextPage,(objects as Array<ItemType>?))
        }
        else {
            return (false,nil)
        }
    }
}