How to write a function in Golang to reverse a unicode string using only 1 assignment/operation?

php editor Zimo will take you through how to write a function in Golang to reverse a unicode string using only 1 assignment/operation. Reversing a string is a common operation, but in Golang we can achieve the effect using only 1 allocation/operation in a clever way. This method is based on the fact that strings are immutable. We can convert the string into a rune slice and then reverse the string by exchanging the elements in the slice. Next, let’s take a look at the specific implementation method!

Question content

I need to write my own reverse.Reverse simulation for unicode strings. This is my code:

func Reverse(input string) string {
    runes := []rune(input)

    var result strings.Builder
    result.Grow(len(runes))

    for i := len(runes) - 1; i >= 0; i-- {
        result.WriteRune(runes[i])
    }

    return result.String()
}

But it will result in 2 allocations/operations:

cpu: 11th Gen Intel(R) Core(TM) i7-11850H @ 2.50GHz
BenchmarkReverse
BenchmarkReverse-16       297900              7014 ns/op            1792 B/op          2 allocs/op

How to do only 1 allocation/operation? I know it's possible

And I don't understand why result.Grow(len(runes)) makes 5 allocations/operations and result.Grow(len(input)) - 1 allocation /Action

Workaround

Create strings.Builder with the required capacity. Writes the runes from the source string to the builder in reverse order.

func Reverse(str string) string {
    var result strings.Builder
    result.Grow(len(str))
    for len(str) > 0 {
        r, size := utf8.DecodeLastRuneInString(str)
        result.WriteRune(r)
        str = str[:len(str)-size]
    }
    return result.String()
}

https://www.php.cn/link/6acfe16b984d473723a8495a84e548b7

This answer replicates the functionality in the question. I don't think it makes sense for the results to be displayed to humans as glyphs. For example, combining characters do not combine like raw strings.

Here is a contrived example that illustrates the use of the reverse function: Certain value sets of an application tend to have string keys with common prefixes and uncommon suffixes. Applications can improve the distribution of the string space by reversing the keys.

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