编组时间字段为Unix时间

Question

I want to encode my time.Time fields as numeric Unix time and I would prefer not to implement custom MarshalJSON functions for each and every struct, since I have lots and lots of structs.

So, I tried defining a type alias as such:

type Timestamp time.Time

And implementing MarshalJSON on it like so:

func (t Timestamp) MarshalJSON() ([]byte, error) {
    return []byte(strconv.FormatInt(t.Unix(), 10)), nil
}

But that gives me a t.Unix undefined (type Timestamp has no field or method Unix), which doesn't make sense to me. Shouldn't Timestamp 'inherit' (I know that's probably the wrong term) all functions of time.Time?

I also tried using a type assertion like so:

strconv.FormatInt(t.(time.Time).Unix(), 10)

But that also fails, complaining about an invalid type assertion: invalid type assertion: t.(time.Time) (non-interface type Timestamp on left)

Answer 1

You need to convert your type back to a time.Time to have access to its methods. Named types do not "inherit" the methods of their underlying types (to do that, you need embedding).

func (t Timestamp) MarshalJSON() ([]byte, error) {
    return []byte(strconv.FormatInt(time.Time(t).Unix(), 10)), nil
}

Also, just as a matter of personal preference, I tend to preferred fmt.Sprintf("%v", i) over strconv.FormatInt(i, 10) or even strconv.Itoa(i). Honestly not sure which is faster, but the fmt version seems easier to read, personally.