Well, the only way we have, currently, to say "This function can take either Number, a Char, a Boolean, a String or a JsonElement" is : - to overload each methods (Kotson have loads of methods that can take either one of this types, so that's not a good option) - to take an Any argument and to throw an exception at runtime if the given argument is not one of the supported types.
Both options are not good to me 