Re: [Boost-bugs] [Boost C++ Libraries] #1418: polymorphic archive performance improvement

Subject: Re: [Boost-bugs] [Boost C++ Libraries] #1418: polymorphic archive performance improvement
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2014-09-13 23:14:18

#1418: polymorphic archive performance improvement
-----------------------------------+----------------------------
  Reporter:  Kim Barrett <kab@…>   |      Owner:  ramey
      Type:  Patches               |     Status:  closed
 Milestone:  Boost 1.49.0          |  Component:  serialization
   Version:  Boost Release Branch  |   Severity:  Optimization
Resolution:  invalid               |   Keywords:  Saitec Eclipse
-----------------------------------+----------------------------

Comment (by anonymous):

 Replying to [comment:9 ramey]:
 > "and then a static (or dynamic when debugging) down-cast to the
 polymorphic-archive class."
 >
 > a static downcast from a virtual base is not permitted. see N3797
 paragraph 5.2.9(2)

 Oops.  That does potentially kill off that suggested alternative that
 could be used if there were a common base class.  But since there isn't
 such a base class, it's pretty much moot anyway, just meaning there may
 not be a reason to add such a base class in order to support this
 alternative implementation.  It could be that adding such a base class and
 using a dynamic cast would be an improvement on the current
 implementation.  My recollection of my testing way back then indicated
 that it was cross-casts that were very expensive, and down-casts not so
 bad.  But that was only with (now) fairly old versions of gcc; newer
 versions of gcc or other compilers might be significantly different.

-- 
Ticket URL: <https://svn.boost.org/trac/boost/ticket/1418#comment:11>
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