[capnproto] Declaring an enum with enumerants corresponding to the field tag of a union.

[Johannes Zeppenfeld]

Hi,

I have an interface with a function returning one of several possible value
types in a union:

interface Interface {
getResult @0 () -> (result :Result);

struct Result {
union {
string @0 :Text;
int @1 :Int32;
}
}
}

I would now like to add another function returning an enum indicating the
type that would be returned by the first function:

interface Interface {
# ...

getResultType @1 () -> (type :ResultType);

enum ResultType {
string @0;
int @1;
}
}

Is there some way of achieving this without having to duplicate the Result
union in the ResultType enum? Ideally, getResultType would simply return
the tag type of the Result union.

Thanks!
Johannes