// FindAllGroups returns a map with each match group. The map key corresponds to the match group name.
// A nil return value indicates no matches.
func FindAllGroups(re *regexp.Regexp, s string) map[string]string {
	matches := re.FindStringSubmatch(s)
	subnames := re.SubexpNames()
	if matches == nil || len(matches) != len(subnames) {
		return nil
	}

	matchMap := map[string]string{}
	for i := 1; i < len(matches); i++ {
		matchMap[subnames[i]] = matches[i]
	}
	return matchMap, nil
}

func ExampleFindAllGroups() {
	re := regexp.MustCompile(`(?P<year>\d{4})-(?P<month>\d{2})-(?P<day>\d{2})`)
	matchMap := FindAllGroups(re, "2018-10-11")
	for k, v := range matchMap {
		fmt.Printf("%s: %s\n", k, v)
	}
	// Output:
	// year: 2018
	// month: 10
	// day: 11
}