time: Time Zero MarshalJSON / UnmarshalJSON produces a different object

[simon3z]

It seems that marshaling and unmarshaling a zero time produces an object that is different from the original:

func TestMarshalUnmarshalJSON(t *testing.T) {
        var expected, parsed Time

        body, err := expected.MarshalJSON()
        if err != nil {
                t.Errorf("json.Marshal error = %v", err)
        }

        err = parsed.UnmarshalJSON(body)
        if err != nil {
                t.Errorf("json.Unmarshal error = %v", err)
        }

        if !reflect.DeepEqual(expected, parsed) {
                t.Errorf("json error, expected = %#v, parsed = %#v", expected, parsed)
        }
}

--- FAIL: TestMarshalUnmarshalJSON (0.00 seconds)
        time_test.go:807: json error, expected = time.Time{sec:0, nsec:0x0, loc:(*time.Location)(nil)}, parsed = time.Time{sec:0, nsec:0x0, loc:(*time.Location)(0x6cd2a0)}

[minux]

Parsing a time will get a non-zero location. This is working as intended. You shouldn't use == to compare time.Time's.

[simon3z]

@minux then this looks like a DeepEqual bug

[minux]

No. DeepEqual is documented to use ==.

[simon3z]

@minux exactly, but as you said, it shouldn't if that's not the way to compare Time

[cespare]

@simon3z wrong conclusion.

• DeepEqual uses ==
• time.Times should not be compared with Equal, not ==
• These both cannot change because of the Go 1 compatibility promise
• Therefore DeepEqual should not be used if the structures you're comparing contain time.Times

If you need a DeepEqual that knows about time.Times, you will need to write it.

[simon3z]

@cespare probably a better design would be something like:

type compare func(a1, a2 interface{}) int

DeepCompare(a1, a2 interface{}, fn compare)

do you think it could be something I could write/include in the reflect package?

[cespare]

@simon3z Better deep comparison is interesting, but let's take this to the golang-nuts mailing list.

[rjeczalik]

@simon3z If you really care about comparing times directly (part of larger struct), you can get away by keeping times in the same timezone (like http://play.golang.org/p/GhvxWMgk-x), but it just workarounds the fact they should be compared with http://golang.org/pkg/time/#Time.Equal.