How Do I Iterate Over Runes in a Go String?

Iterating Over Strings by Runes in Go

When iterating over strings in Go, developers often encounter the need to work with runes (Unicode code points) rather than bytes. This is because Go's string type stores bytes, not runes.

Consider the following code snippet:

for i := 0; i < len(str); i++ {
    dosomethingwithrune(str[i]) // takes a rune
}

This snippet is intended to iterate over the characters in the string str, performing some action with each rune. However, accessing str[i] returns a byte, not a rune.

To iterate over the runes in a string, Go provides a range expression specifically for this purpose:

for pos, char := range "日本語" {
    fmt.Printf("character %c starts at byte position %d\n", char, pos)
}

In the example above, the range expression iterates over the runes in the string, assigning the current rune to the variable char and the current byte position to the variable pos.

The advantage of the range expression is that it handles UTF-8 decoding automatically, breaking out individual Unicode code points. This simplifies the task of iterating over the runes in a string while avoiding the potential pitfalls of manual iteration.

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