Swift 3中的嵌套泛型 [英] nested generics in swift 3

问题描述

是否可以在Swift 3中使用泛型执行以下操作?

is it possible to do following in Swift 3 with generics ?

class BaseModel {} 
class Human : BaseModel {
var name = ""
}

class BaseService<T: BaseVM<BaseModel>> {
   //init viewmodel with generic model
}

class BaseVM<T: BaseModel> {}

class HumanVM: BaseVM<Human> {
var name = ""
init(model : Human) {
    super.init()
    name = model.name
  }
}

class HumanService: BaseService<HumanVM> {}

我想做的是在baseService中使用通用模型初始化viewModel.

what I am trying to do is initializing viewModel with generic model in baseService.

推荐答案

是的，您可以嵌套泛型.您遇到的问题是此行:

Yes, you can nest generics. The problem with what you have is this line:

class BaseService<T: BaseVM<BaseModel>> { ...

在这里您已经说过BaseService必须使用继承自BaseVM的类型进行初始化，该类型的通用 IS BaseModel.如果希望BaseService能够采用从BaseVM继承的类型，而该类型的模型是从BaseModel继承的，则必须采用以下方式:

Here you've said BaseService must be initialized with a type that inherits from BaseVM whose generic IS BaseModel. If you want BaseService to be able to take a type that inherits from BaseVM whose model inherits from BaseModel, you'd have to do it this way:

class BaseService<T: BaseModel, U: BaseVM<T>> { ...

这是您上面编译的版本:

Here is a version of what you have above that compiles:

class BaseModel {}

class BaseVM<T: BaseModel> {}

class BaseService<T: BaseModel, U: BaseVM<T>> {
    //init viewmodel with generic model
}

class Human : BaseModel {
    var name = ""
}

class HumanVM: BaseVM<Human> {
    var name = ""
    init(model : Human) {
        super.init()
        name = model.name
    }
}

class HumanService: BaseService<Human, HumanVM> {}

描述这些关系的另一种方法是使用具有AssociatedTypes的协议.您的代码如下所示:

An alternate approach to describing these relationships would be to use Protocols with AssociatedTypes. Your code would look something like this:

protocol Model {}

protocol BaseVM {
    associatedtype VMModel : Model
}

protocol BaseService {
    associatedtype ServiceVM : BaseVM
}

class Human : Model {
    var name = ""
}

class HumanVM : BaseVM {
    typealias VMModel = Human
}

class HumanService : BaseService {
    typealias ServiceVM = HumanVM
}

在不了解您要解决的问题的更多信息的情况下，我无法说出哪个更合适.

Without knowing more about what problem you're trying to solve, I can't say which is more appropriate.

编辑我仍然不太清楚这如何适用于MVVM模式，但是，如果涉及到视图，则可能需要基于Protocol的解决方案，以便您可以使其符合UIView.

EDIT I'm still not totally clear how this is applicable to the MVVM pattern, but probably, if views are involved, you'd want a Protocol-based solution so that you could make UIView conform to it.

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