[go-nuts] Unexpected panic with gob encoding of anonymous *time.Time values

On Tuesday, January 5, 2016 at 9:29:49 PM UTC-8, Larry Clapp wrote:

This works: http://play.golang.org/p/nUENUMDM7x

time.Time field is called T

output is
"Pythagoras"
"Treehouse"

So far so good.

This doesn't seem to work: http://play.golang.org/p/tooXqJ5Eio

time.Time field is anonymous

output is
""
""

That's odd.

This panics with a nill dereference: http://play.golang.org/p/kGoY9QA6fG

*time.Time field is anonymous (note: pointer to time.Time)

output is
panic: runtime error: invalid memory address or nil pointer dereference
[recovered]
[...]

Ouch.

Am I doing something wrong?

Thanks!

-- Larry

On Di, 2016-01-05 at 21:29 -0800, Larry Clapp wrote:
This works: http://play.golang.org/p/nUENUMDM7x

time.Time field is called T

output is
"Pythagoras"
"Treehouse"

So far so good.

This doesn't seem to work: http://play.golang.org/p/tooXqJ5Eio

time.Time field is anonymous

output is
""
""

That's odd.

This panics with a nill dereference: http://play.golang.org/p/kGoY9QA
6fG

*time.Time field is anonymous (note: pointer to time.Time)

output is
panic: runtime error: invalid memory address or nil pointer
dereference [recovered]
[...]

Ouch.

Am I doing something wrong?

Thanks!

-- Larry

--
You received this message because you are subscribed to the Google
Groups "golang-nuts" group.
To unsubscribe from this group and stop receiving emails from it,
send an email to [email protected].
For more options, visit https://groups.google.com/d/optout.

On Wednesday, January 6, 2016 at 1:16:11 PM UTC-5, mb0 wrote:

hi larry,

when embedding time.Time you will also promote its custom methods
GobDecode and GobEncode to your types P and Q. if you then try to
encode and decode using gob the package will see that your types
implement the GobDecoder and GobEncoder interface and only call those.

that is why the name fields seems to be ignored.

the easy solution is not to embed a time.Time or otherwise implement
the encoding and encoding/gob interfaces to encode and decode your
types on your own instead of calling the implementation of time.Time.

hope that helps

On Thu, Jan 7, 2016 at 5:32 AM, Larry Clapp wrote:
Ah, I hadn't thought of that. Thanks!

In general that behavior is a good thing, but in the specific case of
gob.Encode it seems like it'd always be wrong. Is there some type assert
that gob.Encode or time.GobEncode could do that could keep it from
happening? That is, it seems like time.GobEncode should be able to realize
that it's being asked to encode something that's not a time.Time and panic
appropriately, or something.