Re: [Boost-bugs] [Boost C++ Libraries] #11229: vector incorrectly copies move-only objects using memcpy

Subject: Re: [Boost-bugs] [Boost C++ Libraries] #11229: vector incorrectly copies move-only objects using memcpy
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2015-12-02 14:30:48

#11229: vector incorrectly copies move-only objects using memcpy
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  Reporter:  joseph.thomson@…  |      Owner:  igaztanaga
      Type:  Bugs              |     Status:  new
 Milestone:  To Be Determined  |  Component:  move
   Version:  Boost 1.58.0      |   Severity:  Problem
Resolution:                    |   Keywords:
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Comment (by joseph.thomson@…):

 Actually, as far as I can see, the workaround will result in incorrect
 behaviour. It's been a while since I filed the original ticket, so I can't
 remember all the details, but I assume that the workaround exists to
 emulate the old (incorrect) behaviour of GCC on Clang.

 Implicitly generated, `default`ed and `delete`d copy constructors are
 ''all'' trivial. Thus, `boost::has_trivial_copy` should be true for a
 `std::unique_ptr`. This reflects the new, ''correct'' behaviour of
 `__has_trivial_copy` in GCC 4.9. However, to be trivially copy
 constructible, a class must:

 * have no non-trivial copy constructors, and
 * be copy constructible.

 A `std::unique_ptr` is not copy constructible, even thought it has a
 trivial (`delete`d) copy constructor, so the standard library function
 `std::is_trivially_copy_constructible` should be false for a
 `std::unique_ptr`.

 What I'm saying is that, if what you report is accurate, the behaviour of
 `boost::has_trivial_copy` is currently wrong for both GCC ''and'' Clang.
 It seemingly behaves like `std::is_trivially_copy_constructible`.

-- 
Ticket URL: <https://svn.boost.org/trac/boost/ticket/11229#comment:10>
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