Re: [Boost-bugs] [Boost C++ Libraries] #3996: Enable use of BOOST_FOREACH over const-ref of noncopyable ptr_containers

Subject: Re: [Boost-bugs] [Boost C++ Libraries] #3996: Enable use of BOOST_FOREACH over const-ref of noncopyable ptr_containers
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2010-06-25 00:20:41

#3996: Enable use of BOOST_FOREACH over const-ref of noncopyable ptr_containers
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  Reporter:  Kazutoshi Satoda <k_satoda@…>              |       Owner:  nesotto                     
      Type:  Patches                                    |      Status:  new                         
 Milestone:  Boost 1.43.0                               |   Component:  ptr_container               
   Version:  Boost 1.42.0                               |    Severity:  Problem                     
Resolution:                                             |    Keywords:  BOOST_FOREACH is_noncopyable
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Comment (by Kazutoshi Satoda <k_satoda@…>):

 Replying to [comment:2 eric_niebler]:
 > ... and will lead to ODR violations when different translation units see
 different specializations of foreach::is_noncopyable.

 How different specializations of foreach::is_noncopyable<> can be seen
 for a !ValueType which is required to be complete for the instantiation
 of foreach::is_noncopyable<!ValueType> in my patch?

 I can imagine a case where the specialization of
 foreach::is_noncopyable<!ValueType> is provided in a separate header
 from one which defines !ValueType. But in such case, the problem is in
 !ValueType; the same problem can be caused without my patch.

 > Instead, define a partial specialization of foreach::is_noncopyable<
 reversible_ptr_container<...> >

 Providing a specialization of foreach::is_noncopyable<> for a base class
 isn't propagated to derived classes (ptr_vector<...>, ptr_list<...>, ...
 in this case). With that approach, duplicated definitions of
 specialization would be required. I think it's hardly acceptable,
 especially thinking users can define their own ptr_container using
 reversible_ptr_container<>.

-- 
Ticket URL: <https://svn.boost.org/trac/boost/ticket/3996#comment:3>
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