How to Iterate Over a String by Runes in Go?

Iterating Over a String by Runes in Go

In Go, you may encounter a situation where you want to iterate over a string by its individual runes, or Unicode code points. You may be tempted to use a traditional for loop with the index i to access each character:

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

However, this approach won't work correctly because str[i] returns a byte (uint8) instead of a rune. To iterate over the string by runes, you need to use the range syntax:

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

This code will print the following output:

character 日 starts at byte position 0
character 本 starts at byte position 3
character 語 starts at byte position 6

As the documentation for Effective Go explains, the range syntax "does more work for you, breaking out individual Unicode code points by parsing the UTF-8." This allows you to work with runes directly, making it easier to perform Unicode-related operations on your strings.

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