Dynamically instantiate generics

Using Swift
2

This is a case for type erasure, which usually can be done pretty easily with protocols.

You would define a new protocol called ViewModelProtocol (to avoid clashing with your existing ViewModel names in the example):

protocol ViewModelProtocol {
    var joints: String { get }
    init()
}

and then conform ViewModel2 to it with just:

extension ViewModel2: ViewModelProtocol { }

and then in your view controller:

class ViewController: UIViewController {
    let model: ViewModelProtocol

    func test() {
        print("Joints \(model.joints)")
    }
}

This is what's known as an "existential" protocol, and is currently only possible with protocols that do not have Self or associatedtype requirements, like your Joint protocol does.

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