How to Correctly Index Characters in Go's UTF-8 Strings?

Character Indexing in Golang Strings: UTF-8 Decoding

Although Golang's string literals are character sequences encoded in UTF-8, indexing individual characters by their position using the array-like syntax string[index] can yield unexpected results. This is because UTF-8 characters can occupy multiple bytes, and indexing by byte position can break the UTF-8 encoding.

To index and retrieve individual characters accurately, Golang offers several options:

Using Unicode Code Points (Runes)

• string([]rune("string")[index]): Convert the string to a slice of runes, where each rune represents a Unicode code point. This approach ensures consistent character indexing regardless of UTF-8 byte position.

Example:

package main

import "fmt"

func main() {
    fmt.Println(string([]rune("HELLO, 世界")[1])) // "E"
    fmt.Println(string([]rune("HELLO, 世界")[8])) // "界"
}

Converting Bytes to Characters

• string("byte"): Convert a single-byte ASCII character to a string. Note that this is only applicable to ASCII characters (the first 128 Unicode characters).

Example:

package main

import "fmt"

func main() {
    fmt.Println(string("HELLO"[1])) // "e"
}

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