Golang: Rune

By Xah Lee. Date: . Last updated: .

What's Rune

“Rune” means Unicode codepoint. (think of it as a character.) It is a jargon golang invented.

When you see the word “rune”, you can think of it as any or all of the following:

[see Golang: Basic Types]

Purpose of Rune

The purpose of rune is similar to character type in some other languages.

What's Codepoint

Unicode gives each character a integer id. This integer id is called codepoint.

Note, not all codepoint are character as we think of. For example, newline, tab, non-breaking-space, right-to-left mark, combining character accents, are all codepoints.

Unicode Standard Notation for Codepoint

Unicode has a standard notation for codepoint, starting with U+ followed by its codepoint in hexadecimal. E.g.

Rune Literal

A “rune literal” is a syntax to represent one Unicode character. Like this:

'c' → rune literal. Where the c is 1 single Unicode character. (but may be presented by escape sequence)

All of the following are rune values.

To see all backslash escapes, see Golang: String Backslash Escape

Print a rune in decimal, hex, and standard unicode notations

package main

import "fmt"

func main() {

	// print a rune in decimal, hex, and standard unicode notations

	var capA = 'A'

	fmt.Printf("%d %x %U\n", capA, capA, capA) // 65 41 U+0041
}

Print Rune

Rune is codepoint, thus is a integer.

The following Printf formats work with integer:

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, you use slice type instead. (Slice is a variable length array.) A slice of rune is common, and can be converted to string.

[see Golang: Slice]

[see Golang: String as Chars]

Reference

The Go Programming Language Specification - The Go Programming Language#String_literals

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Golang

  1. Compile, Run
  2. Source Encoding
  3. Package, Import
  4. Comment
  5. Print
  6. String
  7. String Backslash Escape
  8. Rune
  9. Variable
  10. Zero Value
  11. Constant
  12. If Then Else
  13. Switch/Case
  14. Loop
  15. Basic Types
  16. Array
  17. Slice
  18. Map
  19. Struct
  20. Function
  21. Pointer
  22. String as Chars
  23. regexp
  24. Read File
  25. Write to File
  26. Walk Dir
  27. Check File Exist
  28. System Call
  29. Get Script Path
  30. Pointer
  31. Defer
  32. Random Number

Examples

  1. Match Any Regexp
  2. Find Replace
  3. Validate Links
  4. Generate Sitemap

Reference

  1. Go Spec