Question

i have some problems creating a own type Date based on type time.Time

i tried to create the Date type as follows:

type Date time.Time

func (d Date) UnmarshalJSON(buf []byte) error {
    var s string
    json.Unmarshal(buf, &s)
    t, err := time.Parse(timeLayout,s)
    d= Date(t)
    return err
}

func (d Date) MarshalJSON() ([]byte, error) {
    b,_ := json.Marshal(d.Format(timeLayout))
    return b,nil
}

this itself works, i can store this Date as a time.Time in AppEngine Datastore.
the marshaling itself also works,
but is not working is: then when unmarshal from json, the Date d is filled with the value.
this is, as i understand right, because the unmarshalJson function create a copy of Date.

so when i change the unmarshalJson function to use a Pointer to Date
then i cant use:

d=Date(t)

so first question, is there a solution how todo this ?

what i have done now is to rewrite the Code as follows:

type Date struct {
    t time.Time
}

func (d *Date) UnmarshalJSON(buf []byte) error {
    var s string
    json.Unmarshal(buf, &s)
    t, err := time.Parse(timeLayout,s)
    d.t = t
    return err
}

func (d Date) MarshalJSON() ([]byte, error) {
    b,_ := json.Marshal(d.t.Format(timeLayout))
    return b,nil
}

this works, but in this case Date is not an extending type of time.Time its just a wrapper to a time.Time type.

is there a better solution todo this ? im still new to go.

i need this Date type, to have a Date only json formated type, because Chrome only supports the html5 type: date and not datetime.
and method overriding is not possible in go (means to override the un/marshalJson methods of type time.Time ) ?

thanks

Answer 1

Totally untested code:

type Date time.Time

func (d *Date) UnmarshalJSON(buf []byte) error {
        var s string
        json.Unmarshal(buf, &s)
        t, err := time.Parse(timeLayout, s)
        *d = *(*Date)(&t)
        return err
}

func (d *Date) MarshalJSON() ([]byte, error) {
        b, _ := json.Marshal(d.Format(timeLayout))
        return b, nil
}