Custom Date type with format YYYY-MM-DD and JSON decoder (Parser) and encoder (Unmarshal and Marshal methods)

ISODate.go

//ISODate struct
type ISODate struct {
	Format string
	time.Time
}

//UnmarshalJSON ISODate method
func (Date *ISODate) UnmarshalJSON(b []byte) error {
	var s string
	if err := json.Unmarshal(b, &s); err != nil {
		return err
	}
	Date.Format = "2006-01-02"
	t, _ := time.Parse(Date.Format, s)
	Date.Time = t
	return nil
}

// MarshalJSON ISODate method
func (Date ISODate) MarshalJSON() ([]byte, error) {
	return json.Marshal(Date.Time.Format(Date.Format))
}