A Tour of Go Exercise: rot13Reader https://tour.golang.org/methods/23

README.md

Some simple points that I think this code looks great:

• Doesn't need any additional function(s)

• Concise if case error handling, instead of:

  ...
  if err != nil {
      return nil, err
  }
  // do the 13-rotation
  return l, nil

• Only 2 switch cases: lower and upper cases

  • Utilize mod (%) instead of dividing to 'A'-'M' and 'N'-'Z' additional cases

• Use the character representation ('A', 'Z', 'a', 'z') instead of others, such as 65 (decimal ascii of 'A'), 0x41 (hex ascii of 'A'), etc

• Arrange the range cases to looks like comparison chaining 'A' <= b[i] <= 'Z'

rot13.go

package main

import (
    "io"
    "os"
    "strings"
)

type rot13Reader struct {
    r io.Reader
}

func (r13 rot13Reader) Read(b []byte) (int, error) {
    l, err := r13.r.Read(b)
    if err == nil {
        for i := range b {
            switch {
                case 'A' <= b[i] && b[i] <= 'Z':
                    b[i] = (b[i] - 'A' + 13) % 26 + 'A'
                case 'a' <= b[i] && b[i] <= 'z':
                    b[i] = (b[i] - 'a' + 13) % 26 + 'a'
            }
        }
    }
    return l, err
}

func main() {
    s := strings.NewReader("Lbh penpxrq gur pbqr!")
    r := rot13Reader{s}
    io.Copy(os.Stdout, &r)
}

Another approaches: https://gist.github.com/flc/6439105