ROT13

This cipher obscures the characters in a string. With ROT13, characters are rotated 13 places in the alphabet. Other characters are not changed.

In Go, a method in the strings package can be used to translate strings. This is the Map method. It receives a func that receives a rune, and returns a translated one.

Example method

First we define the rot13 method. This receives a rune and returns a rune. It contains the translation logic for the rotation of characters.

Note The Map method is part of the "strings" package. The first argument is a func that translates a rune.

Result The program correctly applies the rot13 transformation. The input string is obscured.

package main

import (
    "fmt"
    "strings"
)

func rot13(r rune) rune {
    if r >= 'a' && r <= 'z' {
        // Rotate lowercase letters 13 places.
        if r >= 'm' {
            return r - 13
        } else {
            return r + 13
        }
    } else if r >= 'A' && r <= 'Z' {
        // Rotate uppercase letters 13 places.
        if r >= 'M' {
            return r - 13
        } else {
            return r + 13
        }
    }
    // Do nothing.
    return r
}

func main() {
    input := "Do you have any cat pictures?"
    mapped := strings.Map(rot13, input)
    fmt.Println(input)
    fmt.Println(mapped)
}Do you have any cat pictures?
Qb lbh unir nal png cvpgherf?

Some details

In the Go strings package documentation, a ROT13 example is presented for the Map method. This uses more complex logic, with modulo division.

Tip I prefer simpler if-else statements when possible—these are easier to reason about for new developers.

And Simplicity, I think, is more important than having fewer lines of code in a method.

For ROT13 methods, a translation method is usually the clearest approach. A new string could be built up, in a loop over the characters, but this is less clear.

Detail Methods like strings.Map are ideal for transforming strings based on characters.

Summary

ROT13 is not a secure cipher. It can easily be reversed. But it might help reduce casual snooping on a piece of text. And it helps us learn about string transformation methods.