[Boost-bugs] [Boost C++ Libraries] #4367: Proposed fix for test_thread_move_return.cpp

Subject: [Boost-bugs] [Boost C++ Libraries] #4367: Proposed fix for test_thread_move_return.cpp
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2010-06-22 19:16:46

#4367: Proposed fix for test_thread_move_return.cpp
---------------------------------------+------------------------------------
 Reporter:  sergey.sprogis@…           |       Owner:         
     Type:  Bugs                       |      Status:  new    
Milestone:  Boost 1.44.0               |   Component:  None   
  Version:  Boost 1.44.0               |    Severity:  Problem
 Keywords:  test_thread_move_return    |  
---------------------------------------+------------------------------------
 Bug description:
 ----------------

 The original statement in test_thread_move_return.cpp (Line 16):

   return boost::move(t);

 triggered the following error message in Sun C++ compiler (this compiler
 assumes that Boost has fix #4305 for boost/thread/detail/thread.hpp):

 ============================================
 "test_thread_move_return.cpp", line 16: Error: Cannot use
 boost::detail::thread_move_t<boost::thread> to initialize boost::thread
 without "boost::thread::boost::thread(const boost::thread&)";.
 1 Error(s) detected.
 ============================================

 and the same test built with gcc-4.4.4 also failed in a similar way

 ============================================

 test_thread_move_return.cpp: In function 'boost::thread
 make_thread_move_return(boost::thread::id*)':
 test_thread_move_return.cpp:16: error: no matching function for call to
 'boost::thread::thread(boost::thread)'
 ../../../boost/thread/detail/thread.hpp:202: note: candidates are:
 boost::thread::thread(boost::detail::thread_move_t<boost::thread>)
 ../../../boost/thread/detail/thread.hpp:150: note:
 boost::thread::thread()
 ../../../boost/thread/detail/thread.hpp:108: note:
 boost::thread::thread(boost::thread&)
 ============================================

 Sun compiler reports the failure because for the following reason.

 After finding  user-defined copy constructor in
 boost/thread/detail/thread.hpp  (line 108)  thread(thread&); compiler
 does not provide the default copy constructor with  'const' qualifier like
 thread(const thread&).

 Then later, when compiler processes test's return statement (line 16)

   return boost::move(t);

 a copy constructor is needed to return the temporary  thread  object by
 value  from  make_thread_move_return(),  but  there  is  no viable copy
 constructor. The existing copy constructor cannot be used because  it's
 not  allowed  to  bind  an  rvalue  (the  temporary thread object) to a
 non-const reference. (Std 2003 13.3.3.1.4:3 )

 So, the result is an error message  mentioned above.

 Meantime, after replacing

 return boost::move(t);

 with

 return boost::thread(boost::move(t));

 compiler does not need copy constructor to create the result object,
 only  user-defined   conversion constructor thread(thread_move_t) is
 used (Std 2003 8.5/14).

-- 
Ticket URL: <https://svn.boost.org/trac/boost/ticket/4367>
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