A Modest Proposal

["David M. Malon" <malon@anl.gov>]

I'm in the middle of tracking down a bug in which the Query Object - Query 
Estimator duo throw an exception when PercentComplete() is invoked--someone 
thinks the query state has become invalid before the iterator has received 
all the data.  That's not what I'm writing about, but it motivates this 
note.

-> I propose that accessor functions like PercentComplete, and even things 
-> like minNumEvents, should NOT throw exceptions.  

   They should instead return "innocuous" values, and we should document our 
   way out of any inconsistencies.  I realize that one could make an 
   argument for notifying the user that her query doesn't exist, rather 
   than telling her that it's 0% complete, but if we force a user to wrap 
   every effort to retrieve an integer from our components in try/catch blocks, 
   and kill her code whenever anything goes even slightly awry if she fails to 
   do so, we will win no fans (...and I want people to LIKE us; well, me, 
   anyway).  

   Consider the single line 
 
 cout<<"iterator returned "<<OOI.numFiles()<<" and "<<OOI.numRefs()<<" refs.";

   Do we want to require that the user write: 
  
************************************************
  
   int nFiles = 0;
   int nRefs = 0;
   cout<<"iterator returned ";
   try {
    nFiles = OOI.numFiles(); 
   }
   catch(...) {
//   "Switch" block to set nFiles or terminate cleanly, depending upon the 
//   particular exception, should go here.
   }
   cout<<nFiles<<" and ";
   try {
    nRefs = OOI.numRefs(); 
   }
   catch(...) {
//   "Switch" block to set nFiles or terminate cleanly, depending upon the 
//   particular exception, should go here.
   }
   cout<<nRefs<<" refs.";

************************************************

   Imagine doing this every time you want to touch a datum!  No one wants 
   to code like this, and I don't believe that doing so improves software 
   quality.

   I am happy to propose that users wrap query construction, estimation, and 
   execution in try/catch blocks, but simple accessors?  

What do you think?

David