types.Date
is a wrapper around time.Time that allows for JSON marshaling a date string formatted as "2006-01-02".
d1 := types.NewDate(time.Now()) // returns *types.Date
d2 := types.DateFromTime(time.Now()) // returns types.Date
d3, err := types.NewDateFromString("2019-01-01") // returns *types.Date, error
d4, err := types.DateFromString("2019-01-01") // returns types.Date, error
d5 := types.MustNewDateFromString("2019-01-01") // returns *types.Date and panics on error
d6 := types.MustDateFromString("2019-01-01") // returns types.Date and panics on error