https://github.com/isucon/isucon7-qualify/blob/5cc8fe024a76c823931abaeb28d7cc92d1ffd9bc/bench/src/bench/urlcache/cache.go#L61 を見て動作検証

test.go

package main

import (
	"fmt"
	"github.com/marcw/cachecontrol"
	"strings"
)

func main() {
	ccs := []string{"public", "max-age=315360000"}
	directive := strings.Join(ccs, " ")
	cc := cachecontrol.Parse(directive)
	fmt.Println("# publicが先だとpublic扱いにならない")
	fmt.Println(ccs)
	fmt.Println(cc.Public())

	ccs2 := []string{"max-age=315360000", "public"}
	directive2 := strings.Join(ccs, " ")
	cc2 := cachecontrol.Parse(directive2)
	fmt.Println("# publicが後だとpublic扱いになる")
	fmt.Println(ccs2)
	fmt.Println(cc2.Public())

	ccs3 := []string{"public", "max-age=315360000"}
	directive3 := strings.Join(ccs, " ")
	cc3 := cachecontrol.Parse(directive3)
	fmt.Println("# publicが先でもカンマでJoinするとpublic扱いになる")
	fmt.Println(ccs3)
	fmt.Println(cc3.Public())
}

結果：

$ go run test.go
# publicが先だとpublic扱いにならない
[public max-age=315360000]
false
# publicが後だとpublic扱いになる
[max-age=315360000 public]
false
# publicが先でもカンマでJoinするとpublic扱いになる
[public max-age=315360000]
false