从非协议，非类类型“ V”继承

Question

I'm trying to define a class like

class x<V,M : V> {}

Which V will be a protocol when defining a new class that extends x but compiler says:

Inheritance from non-protocol, non-class type 'V'

My real example:

class ListController
    <RequestModel,  FillerProtocol , ResultModel, Cell>: BaseViewController
    where
    ResultModel : FillerProtocol,
    Cell: BaseCell<FillerProtocol>,
    RequestModel: ExtendableByBaseListRequestModel {}

Which cause this error:

Type 'ResultModel' constrained to non-protocol, non-class type 'FillerProtocol'

Answer 1

What you are trying to accomplish is not possible using generics. First you'd have to be able to express that your generic parameter V is a protocol or a non-final class. This is not possible. But this restriction is necessary for the constraint M: V to make any sense.

You might have more luck modeling your problem using protocols with associated types, maybe like this:

protocol FillerProtocol {
    associatedtype ResultModel
}

class ListController<RequestModel,  Filler: FillerProtocol, Cell>: BaseViewController
    where
        Cell: BaseCell<Filler>,
        RequestModel: ExtendableByBaseListRequestModel
{

}

That way you don't even have to specify your ResultModel type, it is defined by your FillerProtocol .