How Do I Modify Strings in Go, Knowing They Are Immutable?

Altering Strings in Go: A Practical Solution

In Go, strings are immutable, meaning their contents cannot be modified once created. This can be frustrating when attempting to alter an existing string, but there is a simple solution using the fmt package.

Consider the following code:

<code class="go">package main

import "fmt"

func ToUpper(str string) string {
    new_str := str
    for i := 0; i < len(str); i++ {
        if str[i] >= 'a' && str[i] <= 'z' {
            chr := uint8(rune(str[i]) - 'a' + 'A')
            new_str[i] = chr
        }
    }
    return new_str
}

func main() {
    fmt.Println(ToUpper("cdsrgGDH7865fxgh"))
}</code>

This code attempts to uppercase lowercase characters in a string, but you will encounter an error: "cannot assign to new_str[i]". This is because strings are immutable.

To overcome this, we can convert the string to a slice of bytes and alter that instead:

<code class="go">func ToUpper(str string) string {
    new_str := []byte(str)
    for i := 0; i < len(str); i++ {
        if str[i] >= 'a' && str[i] <= 'z' {
            chr := uint8(rune(str[i]) - 'a' + 'A')
            new_str[i] = chr
        }
    }
    return string(new_str)
}</code>

Here, []byte(str) creates a byte slice from the string, and string(new_str) converts the modified byte slice back to a string.

With this change, you can now alter strings and covert lowercase characters to uppercase:

fmt.Println(ToUpper("cdsrgGDH7865fxgh")) // Output: CDSRGgdh7865FXGH

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