## Why Can\'t I Modify a String in Place in Go?

Why can't I modify a string in place in Go?

Strings in Go are immutable, meaning that once created, you cannot modify their contents. This is evident from the following error: "cannot assign to new_str[i]".

To change the contents of a string, you must first cast it to a []byte slice. Unlike strings, byte slices are indeed mutable. You can then perform your desired modifications on the byte slice and cast it back to a string using the string(...) function.

Here's a modified version of your code that uses byte slices to change lowercase characters to uppercase:

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

Now, when you call ToUpper("cdsrgGDH7865fxgh"), it will correctly convert all lowercase characters to uppercase.

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