Go Rune

Runes

In old programming languages, such as C, there is no difference between a character and a byte, that is char and byte are the same type. As a reminder, a byte is a sequence of 8 bits, whose value can be between 0 and 255.

However, in Go, there is the concept of a rune which is a character that may be represented by more than one byte. For example, the character é is represented by two bytes: 0xc3 and 0xa9. This is a trick used to represent characters that are not in the original ASCII table (the characters used by American computers in the 1960s).

Thus a slice of bytes and a slice of runes are not the same thing.

var s string = "é"
fmt.Println(len(s)) // 2

var s string = "é"
fmt.Println(len([]rune(s))) // 1

Rune literals

A rune literal is a single character enclosed in single quotes, for example 'Ñ' or '€'. You can also use the \u escape sequence to represent a rune, for example \u00A1 or \u03B2 in case you don't have the character on your keyboard.

They can be asign to a variable of type rune:

var r rune = 'Ñ'

The len() function

Note that the example in the introduction to determine the length of a string only works with strings that can be converted to runes, that is strings of a single (possibly multi-byte) character.

Finding the length of rune

Here is the correct way to determine the length of a string in runes:

package main

import (
	"fmt"
	"unicode/utf8"
)

func main() {
	fmt.Println(utf8.RuneCountInString("Hello"))     // 5
	fmt.Println(utf8.RuneCountInString("Hello, 世界")) // 9

}

Output

5
9