How Do Runes Work in Go: A Deep Dive into Unicode Code Points and Case Conversion?

Demystifying Runes in Go

A Deeper Understanding

Runes are alias for int32 data type in Go, representing Unicode codepoints. This means that each character in a string is internally represented by a 32-bit integer. While this may seem unusual at first, it provides several advantages for Go programming.

Rune Swapping

The provided SwapRune function converts runes between uppercase and lowercase. It uses a series of switch cases to compare the rune to specific integer values, which correspond to the Unicode codepoints for 'a', 'z', 'A', and 'Z'. Based on the comparison, it applies a mathematical operation to modify the rune, either adding or subtracting 32 to change its case.

Internals of SwapRune

• r <= 'z': Checks if the rune is between 'a' and 'z' in the Unicode codepoint range.
• &&: Logical AND operator ensures that both conditions in the case are met.
• r - 'a': If both conditions are met, subtracts 32 from the rune to convert it to lowercase.
• 'A' 'a': Adds 32 to convert the rune to uppercase.

Runes in String Operations

The SwapCase function uses the strconv.Map function to apply the SwapRune transformation to each character in a string. This allows for efficient modification of the string's case while maintaining UTF-8 encoding.

Simplified Explanation

Consider the following code using explicit integers:

func SwapRune(r rune) rune {
    switch {
    case 97 <= r && r <= 122:
        return r - 32
    case 65 <= r && r <= 90:
        return r + 32
    default:
        return r
    }
}

Here, the code compares the rune directly to the integer values representing Unicode codepoints, making it clear how the uppercase and lowercase conversion is achieved by mathematical manipulation.

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