A rune in Go is a Unicode code point represented as an int32, used to correctly handle international characters; 1. Use runes instead of bytes to avoid splitting multi-byte Unicode characters; 2. Loop over strings with range to get runes, not bytes; 3. Convert a string to []rune to safely manipulate individual characters; 4. A single rune represents one Unicode character, ensuring proper handling of text like emojis and accented letters.
In Go, a rune is a built-in type that represents a single Unicode code point. It’s essentially an alias for int32, meaning it stores integer values, but it’s used specifically to represent characters in a way that supports international text (like emojis, accented letters, or non-Latin scripts).
Why use runes instead of bytes?
Go strings are made up of bytes, and when you loop over a string using a standard for loop, you get individual bytes — not characters. This works fine for ASCII text (where each character is one byte), but breaks down with Unicode, where a single character (like ' café ' or ' ? ') can be made up of multiple bytes.
For example:
s := "café ?"
for i := 0; i < len(s); i {
fmt.Printf("%c ", s[i])
}This would print each byte, potentially splitting multi-byte characters and giving garbled output.
To handle this correctly, you should use runes:
s := "café ?"
for _, r := range s {
fmt.Printf("%c ", r)
}Now each r is a rune, so you get the correct characters: c a f é ?.
Key points about runes
- A rune = a Unicode code point (e.g., 'A' = U 0041, '€' = U 20AC, '?' = U 1F436)
- Type:
rune(which is justint32under the hood) - Used when you need to process or manipulate individual characters safely in UTF-8 encoded strings
- When you iterate over a string with
range, Go automatically decodes UTF-8 and gives you runes
Converting between strings and runes
You can convert a string to a slice of runes:
r := []rune("hello ?")
fmt.Println(len(r)) // 7 (including the emoji as one rune)And back to a string:
s := string(r)
This is useful when you need to index or modify individual characters in a string.
Summary
- Use
runewhen dealing with Unicode characters in Go - Iterate over strings with
rangeto get runes, not bytes - Convert to
[]runeif you need to manipulate characters safely - Remember:
rune=int32= one Unicode character
Basically, runes are Go’s way of helping you write text-processing code that works correctly across languages and symbols.
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