When submitting queries by the function SubmitQuery(QueryType t, string& plan, pfnQueryResultsListener l, void* lCtx) of drillClientImp class, the listenerContext parameter provides a convenient way of associating returned results with submitted queries.
The way it works is that the calling application passes the context to SubmitQuery and when returning results, processQueryResult passes the context to the queryResultListener callback function. As such, the callback function can associate the returned result with the context.
When we were updating QuerySubmitter example to showcase usage of SubmitQuery with context, we noticed processQueryResult function does not pass the context directly to the queryResultListener callback function; Instead, an instance of DrillClientQueryResult which contains the context as a data member is passed to the queryResultListener. This requires the queryResultListener function, which is implemented in consumers of the C++ Client, to know about the DrillClientQueryResult.
However, DrillClientQueryResult is not in the public API of the C++ Client. Two solutions are imaginable at the first glance: First, passing the context instead of a DrillClientQueryResult, which we implemented and tested it; Second, moving DrillClientQueryResult to the public API; Moving DrillClientQueryResult to the public API does not seem to be desirable as it is internal detail for the C++ Client.
I was wondering what your thoughts are on this.