Hello, Saurabh. I understand what you're trying to do, and that it seems to
make perfect sense. Every instance of a Msg2 also has all the fields of a
Msg1, so why can't it be a special subtype with just some extra data?
Ploymorphism is meant primarily for types where the difference among
parents and subtypes is behavior, but not for differering data fields. See
here <https://en.wikipedia.org/wiki/Circle-ellipse_problem> for a more
detailed explanation why.
On Wednesday, October 19, 2016 at 3:30:22 PM UTC-4, Saurabh Kumar wrote:
>
> Hi,
>
> This question is regarding inheritance in protobuf C++ library. I will
> explain what I am looking for with a concrete example.
>
> I have this message definition:
>
> message MSG1
> {
> required string account = 0;
> required string symbol = 1;
> }
>
> Now I want to extend this message and define a new message like this:
> message MSG2
> {
> required string account = 0;
> required string symbol = 1;
> required int32 id = 2;
> }
>
> You will notice that first two fields of MSG2 are exactly same as MSG1
> (they are intended to be like that). But here I had to copy paste the
> common fields again.
> Can I do something like this?
>
> message MSG2 extends MSG1
> {
> required int32 id = 2;
> }
>
> I have already thought about using it like:
> message MSG2
> {
> required MSG1 msg1 = 0;
> required int32 id = 2;
> }
> But this is not really what I want.
>
> What's the best way to achieve this?
>
> Thanks,
> Saurabh
>
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