[Xapian-tickets] [Xapian] #332: Avoid const_cast in matcher/queryoptimiser.cc

[Xapian]

#332: Avoid const_cast in matcher/queryoptimiser.cc
---------------------+------------------------------------------------------
 Reporter:  richard  |       Owner:  olly     
     Type:  defect   |      Status:  new      
 Priority:  normal   |   Milestone:  1.1.0    
Component:  Matcher  |     Version:  SVN trunk
 Severity:  normal   |   Blockedby:           
 Platform:  All      |    Blocking:           
---------------------+------------------------------------------------------
 Currently (as of revision [11838]), matcher/queryoptimiser.cc performs a
 const_cast in order to produce a Database object from a "const
 Xapian::Database::Internal".  The Database object has various non-const
 methods on it (notably, reopen() and close()) which must not be called on
 the resulting Database object.  The object is only supplied to
 PostingSource subclasses (via the reset() method), so this is probably not
 a problem in practice, but it would certainly be good to tidy this up,
 somehow.

 I've not come up with a good way to tidy it up, yet.  One approach would
 be a Database subclass which overrides the non-const methods of Database
 to return errors - this would not be terribly tidy, but would at least
 allow the API to ensure that non-const methods didn't get called on the
 "const Xapian::Database::Internal" object.

 Another approach would be to create a "DatabaseSnapshot" class, which
 contains all the const methods of Database (which access a constant
 version of the database).  Then we could make Database into a subclass of
 DatabaseSnapshot, or something along those lines.

 Better ideas welcomed!  Marking as 1.1.0 for now, in case the only
 solution we can come up with involves breaking API somewhere.

-- 
Ticket URL: <http://trac.xapian.org/ticket/332>
Xapian <http://xapian.org/>
Xapian