id,summary,reporter,owner,description,type,status,milestone,component,version,severity,resolution,keywords,cc
11229,vector incorrectly copies move-only objects using memcpy,joseph.thomson@…,Ion Gaztañaga,"The behaviour of `__has_trivial_copy` seems to have be corrected in GCC 4.9, such that deleted copy constructors are now considered trivial.  This seems to be in-line with the C++ standard and Clang as explained in this issue:

https://svn.boost.org/trac/boost/ticket/10389

This change seems to have exposed a bug in Boost.Container, where objects are copied using memcpy if they have a trivial copy constructor.  However, memcpy should only be used as an optimization on trivially copyable objects, the requirements for which include no non-trivial move constructors or assignment operators.

Move-only classes like std::unique_ptr have trivial (but deleted) copy constructors, but are not trivially copyable, since they define move operations.

To fix this, I think that boost/container/details/utilities.hpp needs to be changed.  Perhaps something like this:

{{{
template <typename I, typename O>
struct is_memtransfer_copy_assignable
{
   static const bool value = are_contiguous_and_same<I, O>::value &&
      boost::is_copy_assignable< typename ::std::iterator_traits<I>::value_type >::value &&
      boost::has_trivial_assign< typename ::std::iterator_traits<I>::value_type >::value;
};

template <typename I, typename O>
struct is_memtransfer_copy_constructible
{
   static const bool value = are_contiguous_and_same<I, O>::value &&
      boost::is_copy_constructible< typename ::std::iterator_traits<I>::value_type >::value &&
      boost::has_trivial_copy< typename ::std::iterator_traits<I>::value_type >::value;
};
}}}

This is a check for whether the class has a trivial copy constructor/assignment operator, which I believe should be fine.  boost::is_copy_assignable used to exist in Boost 1.58.0, but seems to have been removed in the development trunk for some reason.

Note that _has_trivial_copy still behaves incorrectly in this circumstance in VC++12.  In fact, VC++ seems to have broken boost::is_copy_assignable and boost::is_copy_constructible functions, as well as broken SFINAE detection for copy/move constructors and operators.  Thus, the modification I have above will still work around this problem, but only because all of the functions return the wrong values.",Bugs,closed,To Be Determined,move,Boost 1.58.0,Problem,fixed,,