In this particular example, they don't. They encourage you to define a Cookie struct, construct it with all the fields you know, pass it to the method with

In this particular example, they don't. They encourage you to define a Cookie struct, construct it with all the fields you know, pass it to the method with gok.SetCookie(Cookie{name: "blub", duration: 5000}) and the method should decide what to do based on the fields available