append.go

func appendStringsIfMissing(slice []string, elements ...string) (out []string) {
	out = slice
outer:
	for _, element := range elements {
		for _, e := range slice {
			if e == element {
				continue outer
			}
		}
		out = append(out, element)
	}
	return
}

func appendStringIfMissing(slice []string, element string) []string {
	for _, e := range slice {
		if e == element {
			return slice
		}
	}
	return append(slice, element)
}