Instantiate ViewModel data with Generic Protocols - ios

Question

So basically I'm trying to define one generic viewmodel protocol from which I would be able to define all other viewmodels ... but data in them would need to stay generic ... lets say I define protocol like below:
protocol GenericVMProtocol {
associatedtype T
var items: [T] { get }
}
Next, I conform my VM to it and define data:
class VM: GenericVMProtocol {
typealias T = String
var items: [String] = ["A", "B" , "C"]
}
For now everything is working as expected, but problems happen when I want to conform my VC to VMProtocol like so:
class VC: UIViewController {
var vm: GenericVMProtocol
override init(nibName nibNameOrNil: String?, bundle nibBundleOrNil: Bundle?) {
vm = VM()
super.init(nibName: nil, bundle: nil)
}
func items() {
print(vm.items)
}
required init?(coder aDecoder: NSCoder) {
fatalError()
}
}
Im getting error:
Protocol 'GenericVMProtocol' can only be used as a generic constraint
because it has Self or associated type requirements
... And I must say I'm pretty clueless if I'm missing some logic or my thinking is wrong .. so I would appreciate any help! Tnx :)

Answer 1

This is a PAT (protocol associated type) problem you cannot directly use GenericVMProtocol as type because again it has associated type requirements in your case
I dont know if the following will help you but the correct way to use a protocol with generic constraint is as follow :
protocol GenericVMProtocol {
associatedtype T
var items: [T] { get }
init()
}
class VM: GenericVMProtocol {
typealias T = String
var items: [String] = ["A", "B" , "C"]
required init() {}
}
class VC<T>: UIViewController where T:GenericVMProtocol {
var vm: T
override init(nibName nibNameOrNil: String?, bundle nibBundleOrNil: Bundle?) {
vm = T()
super.init(nibName: nil, bundle: nil)
}
func items() {
print(vm.items)
}
required init?(coder aDecoder: NSCoder) {
fatalError()
}
}