Golang: Rune

What is Rune

Rune means Unicode Codepoint. (think of it as a character type.) It is a jargon golang invented.

A rune is ALL of the following. Which meaning you pick depends on context:

• A integer, with possible values from 0 to 2^32 -1.
• A golang type, with keyword rune. It is alias to the type int32.
• A Unicode Codepoint.
• A character.

Purpose of Rune

The purpose of rune type is to directly represent one character. It is essentially a character type, just with a fancy name.

Rune Literal

A Rune Literal is a syntax to represent one Unicode character in golang. Like this: 'c', where the c is 1 single Unicode character. (but may be presented by escape sequence)

All of the following are rune values.

• var capA = 'A'
• var heart = '♥'
• var omg = '😂'
• var newline = '\n' 〔see Golang: String Backslash Escape〕
• var heart = '\u2665' same as '♥'
• var omg = '\U0001F602' same as '😂'

package main

import "fmt"

func main() {

	// print a rune in decimal, hexadecimal, and standard unicode notation
	var xx = 'A'
	fmt.Printf("%d %x %U\n", xx, xx, xx) // 65 41 U+0041
}

Print Rune

Since a rune value is a integer, we can use Printf formats that converts integer to string.

• Golang: Printf Verbs

%c

print as the byte sequence of the character in Unicode: UTF-8 Encoding .

%q

print in golang rune syntax. Sample output: 'a'.

%U

print in Unicode notation. Sample output: U+03B1.

%d

print as integer in decimal notation.

%x

print as integer in Hexadecimal Notation.

package main

import "fmt"

// print rune in different formats

func main() {
	var x = '😂'

	fmt.Printf("%c\n", x) // 😂
	fmt.Printf("%q\n", x) // '😂'
	fmt.Printf("%U\n", x) // U+1F602

	fmt.Printf("%b\n", x) // 11111011000000010
	fmt.Printf("%o\n", x) // 373002
	fmt.Printf("%d\n", x) // 128514
	fmt.Printf("%x\n", x) // 1f602
}

Rune Sequence

Value of rune type is just a single char.

For a sequence of chars, use Array or Slice. A slice of rune is common, and can be converted to string. 〔see Golang: String, Byte Slice, Rune Slice〕