gistfile1.txt

protocol ProtocolA {
    init()
}

class classA : ProtocolA {
    required init() {
        
    }
}

func create<T: ProtocolA>(T.Type) -> T? {
    return T()
}

let foo = create(classA) //ok
let bar = create(String) //error "Cannot invoke 'create' with no arguments"