You can only have mutually-recursive messages if they are defined in the
same file.
I don't think your approach would work quite as you expect anyway. Message
fields are not pointers, so you can't have a recursive object at runtime.
That is, if you do:
message A {
optional B b = 1;
}
message B {
optional A a = 1;
}
If you have an instance of A called foo, you *cannot* make it so that
foo.b.a == foo -- foo.b.a is an entirely different object.
If you need to be able to down-cast (that is, given a pointer to the
superclass, you need a way to get a pointer to the subclass), then you need
the superclass to look like:
message Superclass {
// One of the following will be filled in.
optional Subclass1 subclass1 = 1;
optional Subclass2 subclass2 = 2;
...
}
You can use extensions instead of normal fields, which is often useful for
these cases. Other than that, though, there's no other option. You cannot
convert a Subclass1 back to a Superclass, so you have to pass around
pointers to the Superclass itself and simply say "This object must contain a
subclass1".
In general, you may find that trying to shoe-horn a concept of inheritance
into protocol buffers doesn't work well. Unfortunately, classic
object-oriented inheritance does not translate well to message formats sent
over the wire. Extensions, on the other hand, are very straightforward on
the wire, which is why that is what protocol buffers provides.
On Thu, May 28, 2009 at 10:16 AM, <[email protected]> wrote:
>
> Just to complete the view, i' m trying to simulate inheritance.
>
> Derived Classes need to have a required field to their mother (so that
> when i'm using directly a derived class i can set the super class
> fields).
>
> And abstract classes need to have an optional field
> to all possible derived classes (emulate the fact that a super class
> can become any sort of derived class).
>
> I can bypass the problem by using "extend" in the derived classes
> message file (extending field of the super class, adding an optional
> field of themselves) , so that only the derived classes side need to
> use import.
>
> but i was wondering if there was another way to do so ??
>
> cheers,
>
> Pascal ly
>
>
> On May 28, 6:51 pm, [email protected] wrote:
> > Hi,
> >
> > i need a message A to have a field with a message B, and at the same
> > time i need messages B to have a field to message A, how to avoid
> > recursive imports ??
> >
> > cheers,
> >
> > Pascal Ly.
> >
>
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