UTF-8な日本語文字数を考慮したPrintf("%s")指定方法

main.go

package main

import (
	"fmt"
	"unicode/utf8"
)

func main() {
	hoges := []string{
		"Hello, playground",
		"ハロハロ, playground",
	}

	for _, hoge := range hoges {
		textCount := 30 + ((utf8.RuneCountInString(hoge) - len(hoge)) / 2)
		fmt.Println(textCount)
		format := fmt.Sprintf("%%-%ds %%s\n", textCount)
		fmt.Printf(format, hoge, "Go!")
	}
}

memo.md

Demo