nested generics in swift

 原文链接

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

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

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>> { ...

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> {}

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
}

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

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.