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What the heck is a rune in Golang

luispa profile image LuisPa ・2 min read

Photo by Gerson Repreza on Unsplash

The banner is a Cancún beach because I miss it some much.

Well, let's begin.

If you're familiarized with Golang might you already know what a rune is, but if you wanna clear more, you can continue reading.

In this short post, we will learn why the rune is a type of structure important and powerful in the Golang environment.

Let's start with the origin.

Characters, ASCII and Unicode

The rune type is an alias for int32 and is used to emphasize than an integer represents a code point.

ASCII defines 128 characters, identified by the code points 0–127. It covers English letters, Latin numbers, and a few other characters.

Unicode, which is a superset of ASCII, defines a codespace of 1,114,112 code points. Unicode version 10.0 covers 139 modern and historic scripts (including the runic alphabet, but not Klingon) as well as multiple symbol sets.

Strings and UTF-8 encoding

A string is a sequence of bytes, not runes.

However, strings often contain Unicode text encoded in UTF-8, which encodes all Unicode code points using one to four bytes. (ASCII characters are encoded with one byte, while other code points use more.)

Since Go source code itself is encoded as UTF-8, string literals will automatically get this encoding.

For example, in the string "café" the character é (code point 233) is encoded using two bytes, while the ASCII characters c, a and f (code points 99, 97 and 102) only use one:

fmt.Println([]byte("café")) // [99 97 102 195 169]
fmt.Println([]rune("café")) // [99 97 102 233]

Important points

  • Golang uses runes to manage Unicode chars, instead to limit the development only for ASCII values.
  • The importance to know this difference is to manage better the iteration between elements, and have a more clear scope of spaces, values, and differences between a string and a rune.
  • All of these values are bits and bytes as well, but it's better if we know when to use it and where to use it.

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Happy coding!

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