My complain with nil in Go is that there are different kinds of it as a nil pointer to a struct is not equal to a nil pointer of the interface it implements and

My complain with nil in Go is that there are different kinds of it as a nil pointer to a struct is not equal to a nil pointer of the interface it implements and code like https://play.golang.org/p/NwKvIztXwP https://play.golang.org/p/NwKvIztXwP prints false. This is the reason for the rule of always returning error type in Go, not a pointer to detailed struct error. That leads to an ugly code when a check for non-nil err is followed by a cast.