Re: [Boost-bugs] [Boost C++ Libraries] #10798: boost::movelib::unique_ptr resolves typedef pointer with the deletor's

Subject: Re: [Boost-bugs] [Boost C++ Libraries] #10798: boost::movelib::unique_ptr resolves typedef pointer with the deletor's
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2014-11-25 08:52:27

#10798: boost::movelib::unique_ptr resolves typedef pointer with the deletor's
-------------------------------------------------+-------------------------
  Reporter:  Matteo Settenvini                   |      Owner:  igaztanaga
  <matteo.settenvini@…>                          |     Status:  new
      Type:  Bugs                                |  Component:  move
 Milestone:  To Be Determined                    |   Severity:  Problem
   Version:  Boost 1.57.0                        |   Keywords:
Resolution:                                      |
-------------------------------------------------+-------------------------

Comment (by Matteo Settenvini <matteo.settenvini@…>):

 Unfortunately not, since the deleter I wrote uses a field of the base
 class to determine the runtime type of the object, and resolves a call to
 the right destructor (plus, deallocates memory with the right custom
 allocator). This is needed since we have no virtuality in objects of
 classes that need to be stored in shared memory.

 In other words, I need to use just a deleter for the whole hierarchy of
 classes, and thus its pointer member needs to be the base type. We're
 rolling out our handmade version of virtuality, with virtual tables and
 all that goes with them.

 What I find counter-intuitive from a design standpoint, is that:
   * be it that we have classes Derived < Base.
   * given a Deleter with a member "pointer" as a typedef to Base.
   * defining a unique_ptr<Derived, Deleter> and invoking ::get() results
 in a pointer to Base being returned.

 What is the technical reason of having the pointer typedef of the
 unique_ptr using the pointer member of the deleter, instead than rebinding
 it to allow upcasts?

-- 
Ticket URL: <https://svn.boost.org/trac/boost/ticket/10798#comment:2>
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