format.go
func MustStringFormatter(format string) Formatter {
	f, err := NewStringFormatter(format)
	if err != nil {
		panic("Failed to initialized string formatter: " + err.Error())
	}
	return f
}
func MustStringFormatter(format string) Formatter {
	f, err := NewStringFormatter(format)
	if err != nil {
		panic("Failed to initialized string formatter: " + err.Error())
	}
	return f
}
// MustStringFormatter is equivalent to NewStringFormatter with a call to panic
// on error.