Re: [Boost-bugs] [Boost C++ Libraries] #5381: get_deleter<D>(ptr) needs D to be exactly known

Subject: Re: [Boost-bugs] [Boost C++ Libraries] #5381: get_deleter<D>(ptr) needs D to be exactly known
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2011-04-06 21:32:50

#5381: get_deleter<D>(ptr) needs D to be  exactly known
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  Reporter:  christian.kotz@…           |       Owner:  pdimov   
      Type:  Feature Requests           |      Status:  new      
 Milestone:  To Be Determined           |   Component:  smart_ptr
   Version:  Boost 1.45.0               |    Severity:  Problem  
Resolution:                             |    Keywords:           
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Comment (by steven_watanabe):

 Replying to [ticket:5381 christian.kotz@…]:
 > get_deleter<Base_of_D>(ptr) returns 0.
 >
 > This makes efficient polymorphous COW pointer implementations internally
 based on shared_pointer inefficient, because it is not possible to have
 reference count (deleter) and pointee allocated in one memory block, as is
 done in boost:::make_shared. Note, COW pointer need access to the deleter
 for the clone function at a time later than the constructor.

 I don't understand.  If you want to make something like make_shared, you
 should only need to access the deleter when you're constructing the
 object.  At this point, you need to know the exact type of the deleter
 anyway.  Actually, though, I don't see what you want to do that can't be
 handled by just using make_shared.

-- 
Ticket URL: <https://svn.boost.org/trac/boost/ticket/5381#comment:1>
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