$ cat tpack/tpack.go
package tpack

type Tpack struct {
    Wat int
    asd int
}

$ cat tpack-main.go
package main
import tpack "./tpack"
func main() {
    var tp tpack.Tpack
    tp.Wat = 1
    tp.asd = 1
    }
$ go run tpack-main.go
# command-line-arguments
./tpack-main.go:6: tp.asd undefined (cannot refer to unexported field or method asd)