Rune and UTF-8

Learn Unicode characters with rune and UTF-8 encoding.

Runes and UTF-8

In UTF-8 a character takes 1 to 4 bytes: a is 1, ç 2, € 3 and an emoji 4 bytes. To work at the character level use []rune and unicode/utf8:

s := "çay ☕"
fmt.Println(len(s))                     // 8 bytes
fmt.Println(utf8.RuneCountInString(s))  // 5 characters
r := []rune(s)
fmt.Println(string(r[0]))               // ç

The unicode package

The unicode package classifies runes and recognizes Turkish letters correctly:

for _, r := range "Ğ5 a!" {
    fmt.Println(string(r), unicode.IsLetter(r), unicode.IsDigit(r), unicode.IsUpper(r))
}

Text analysis is done with functions such as unicode.IsSpace, unicode.IsPunct and unicode.ToUpper.

Exercise Reverse it

Write the ters(s string) string function using []rune and print the result of ters("çiçek").

Show example solution

package main

import "fmt"

func ters(s string) string {
    r := []rune(s)
    for i, j := 0, len(r)-1; i < j; i, j = i+1, j-1 {
        r[i], r[j] = r[j], r[i]
    }
    return string(r)
}

func main() {
    fmt.Println(ters("çiçek"))
}

Test yourself

Why is <code>[]rune</code> used to reverse the text "çay"?
- It's shorter
- There is no difference
- Reversing bytes would break ç's two bytes
- []byte isn't supported
Show answer

Reversing bytes would break ç's two bytes — ç is two bytes; reversing at the byte level produces invalid UTF-8. Runes keep characters whole.

Count characters

n := utf8.____("ışık")  // 4

Show answer

n := utf8.RuneCountInString("ışık")  // 4

Character and byte count

a

1 byte
ç

2 bytes
€

3 bytes
😀

4 bytes

Next lesson: Summary - String

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