True. You could work around it by conditionally extending your ViewContainer to have a default constructor (init()), if the type is EmptyView. Then you can write

    var viewContainer2 = ViewContainer<EmptyView>()

But that's probably not what you want is it. Default generic arguments aren't implemented yet, see (https://stackoverflow.com/questions/42015081/can-i-assign-a-...). It would have possibly removed the <EmptyView> aspect. So you always have to give a type to ViewContainer, if you provide no way for the compiler to infer it.