func foo(completionHandler: (String!, unz_file_info, Int, Int)->Void){
    //do whatever you need to
    completionHandler("this is a string", <object of type unz_file_info>, 1, 2)
}

foo(completionHandler: {
    (w:String!, x:unz_file_info, y:Int, z:Int) in

    print(w)
    print(x)
    print(y)
    print(z)
})