I'm currently working on the Go Lang tutorial, but ran into problem with one of the exercises:
https://tour.golang.org/methods/23
The exercise has me implement a ROT13 cipher. I decided to implement the cipher using a map from a byte to its rotated value but I'm not sure of the best way to initialize this map. I don't want to initialize the map using a literal, but would prefer to do it programmatically by looping through an alphabet and setting (key, value) pairs within the loop. I would also like the map to only be accessible from Rot13Reader struct/object and have all instances(?) share the same map (rather than one copy per Rot13Reader).
Here's my current working Go program:
package main
import (
"io"
"os"
"strings"
)
type rot13Reader struct {
r io.Reader
}
var rot13Map = map[byte]byte{}
func (rotr *rot13Reader) Read(p []byte) (int, error) {
n, err := rotr.r.Read(p)
for i := 0; i < n; i++ {
if sub := rot13Map[p[i]]; sub != byte(0) {
p[i] = sub
}
}
return n, err
}
func main() {
func() {
var uppers = []byte("ABCDEFGHIJKLMNOPQRSTUVWXYZ")
var lowers = []byte("abcdefghijklmnopqrstuvwxyz")
var init = func (alphabet []byte) {
for i, char := range alphabet {
rot13_i := (i + 13) % 26
rot13Map[char] = alphabet[rot13_i]
}
}
init(uppers)
init(lowers)
}()
s := strings.NewReader("Lbh penpxrq gur pbqr!")
r := rot13Reader{s}
io.Copy(os.Stdout, &r)
}
Here are the problems I have with this:
- I don't want to have to prepare
rot13Map
inmain()
- I don't want
rot13Map
to be in global scope. - I don't want each copy of a
rot13Reader
to have a separaterot13Map
Is there a way to achieve what I want in Go?