func getNextWildcard(pattern string) (wildcard, _ string) {
	pos := wildcardPattern.FindStringIndex(pattern)
	if pos == nil {
		return "", pattern
	}
	wildcard = pattern[pos[0]:pos[1]]

	// Reach last character or no regexp is given.
	if len(pattern) == pos[1] {
		return wildcard, strings.Replace(pattern, wildcard, `(.+)`, 1)
	} else if pattern[pos[1]] != '(' {
		switch {
		case isSpecialRegexp(pattern, ":int", pos):
			pattern = strings.Replace(pattern, ":int", "([0-9]+)", 1)
		case isSpecialRegexp(pattern, ":string", pos):
			pattern = strings.Replace(pattern, ":string", "([\\w]+)", 1)
		default:
			return wildcard, strings.Replace(pattern, wildcard, `(.+)`, 1)
		}
	}

	// Cut out placeholder directly.
	return wildcard, pattern[:pos[0]] + pattern[pos[1]:]
}
func getNextWildcard(pattern string) (wildcard, _ string) {
	pos := wildcardPattern.FindStringIndex(pattern)
	if pos == nil {
		return "", pattern
	}
	wildcard = pattern[pos[0]:pos[1]]

	// Reach last character or no regexp is given.
	if len(pattern) == pos[1] {
		return wildcard, strings.Replace(pattern, wildcard, `(.+)`, 1)
	} else if pattern[pos[1]] != '(' {
		switch {
		case isSpecialRegexp(pattern, ":int", pos):
			pattern = strings.Replace(pattern, ":int", "([0-9]+)", 1)
		case isSpecialRegexp(pattern, ":string", pos):
			pattern = strings.Replace(pattern, ":string", "([\\w]+)", 1)
		default:
			return wildcard, strings.Replace(pattern, wildcard, `(.+)`, 1)
		}
	}

	// Cut out placeholder directly.
	return wildcard, pattern[:pos[0]] + pattern[pos[1]:]
}
// getNextWildcard tries to find next wildcard and update pattern with corresponding regexp.