How to get all characters in golang unicode range table

main.go

// link to go playground: https://play.golang.org/p/BihbZqsk5Kh

package main

import (
	"crypto/rand"
	"math/big"
	"unicode"
)

func main() {
	println(string(getAllChars(unicode.ASCII_Hex_Digit)))
	println(string(getRandomChar(unicode.ASCII_Hex_Digit)))
}

func getAllChars(table *unicode.RangeTable) []rune {
	res := make([]rune, 0)

	for _, r := range table.R16 {
		for c := r.Lo; c <= r.Hi; c += r.Stride {
			res = append(res, rune(c))
		}
	}
	for _, r := range table.R32 {
		for c := r.Lo; c <= r.Hi; c += r.Stride {
			res = append(res, rune(c))
		}
	}

	return res
}

// maybe you can optimize it, but these are just unicode tricks

func getRandomChar(table *unicode.RangeTable) rune {
	charsSum := getCharsCount(table)

	choosed, err := rand.Int(rand.Reader, big.NewInt(int64(charsSum)))
	if err != nil {
		panic(err)
	}

	return getNChar(table, int(choosed.Int64()))
}

func getNChar(table *unicode.RangeTable, i int) rune {
	for _, r := range table.R16 {
		if i >= charsInR16(r) {
			i -= charsInR16(r)
		} else {
			return rune(r.Lo + r.Stride*uint16(i))
		}
	}
	for _, r := range table.R32 {
		if i >= charsInR32(r) {
			i -= charsInR32(r)
		} else {
			return rune(r.Lo + r.Stride*uint32(i))
		}
	}

	panic("can't get here")
}

func getCharsCount(table *unicode.RangeTable) int {
	var charsSum int

	for _, r := range table.R16 {
		charsSum += charsInR16(r)
	}
	for _, r := range table.R32 {
		charsSum += charsInR32(r)
	}

	return charsSum
}

func charsInR16(r unicode.Range16) int {
	return int((r.Hi-r.Lo)/r.Stride + 1)
}

func charsInR32(r unicode.Range32) int {
	return int((r.Hi-r.Lo)/r.Stride + 1)
}