我的目标是创建一个模块化的网络服务层，可以很容易地进行单元测试。
为了实现这一目标，我简单地从以下协议开始：

protocol NetworkService {
    associatedtype Response
    func fetchData() async throws -> Response
}

然后，我继续创建一个服务来获取新闻提要，如下所示：

struct FetchNewsService: NetworkService {
    typealias Response = [NewsAssetModel]
    
    func fetchData() async throws -> Response {
        guard let fetchNewsURL = URL(string: SystemConstants.NetworkConstants.fetchNewsEndpoint) else {
            throw NetworkError.invalidURL
        }
        
        let urlRequest = URLRequest(url: fetchNewsURL)
        let session = URLSession(configuration: .default)
        
        guard let (data, response) = try? await session.data(for: urlRequest) else {
            // Would need to handle no internet error as well
            throw NetworkError.server
        }
        
        if let httpResponse = response as? HTTPURLResponse,
           httpResponse.statusCode > 400 {
            throw NetworkError.server
        }
        
        guard let newsResponse = try? JSONDecoder().decode(NewsResponseModel.self,
                                                           from: data) else {
            throw NetworkError.decode
        }
        
        return newsResponse.assets
    }
}

在我的视图模型中，我希望请求获取新闻提要项，因此我希望将NetworkService类型注入到视图模型中。

class NewsAssetManager {
    private(set) var newsAssets: [NewsAssetModel] = []
    private var newsService: NetworkService // 1 - error on this line
    
    // 2 - and this line below
    init(withNewsService newsService: NetworkService = FetchNewsService()) {
        
    }
}

在属性声明中得到的第一个错误是Protocol 'NetworkService' can only be used as a generic constraint because it has Self or associated type requirements
我在初始化器中得到的第二个错误也是相同的Protocol 'NetworkService' can only be used as a generic constraint because it has Self or associated type requirements
我做错了什么？我如何修复/改进？

更新泛型

一个三个三个一个
最后一行Cannot convert return expression of type '[NewsAssetModel]' to return type 'T'出现错误

根据评论和答复更新

将Any & Some的组合添加到属性或初始化器中仍然无法消除所面临的编译错误。

我还通过终端和此代码确认，我至少在运行Swift 5.6：

#if swift(>=5.6)
        print("swift 5.6")
#endif