Re: [Boost-bugs] [Boost C++ Libraries] #2823: [fusion] vector copy constructor copies sequence members in different order on different platforms

Subject: Re: [Boost-bugs] [Boost C++ Libraries] #2823: [fusion] vector copy constructor copies sequence members in different order on different platforms
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2010-11-29 04:12:43

#2823: [fusion] vector copy constructor copies sequence members in different order
on different platforms
---------------------------------+------------------------------------------
  Reporter:  dkomisar@…          |       Owner:  djowel 
      Type:  Bugs                |      Status:  new    
 Milestone:  Boost 1.39.0        |   Component:  fusion 
   Version:  Boost 1.38.0        |    Severity:  Problem
Resolution:                      |    Keywords:         
---------------------------------+------------------------------------------

Comment (by grafik):

 I've run into this problem recently, and bugged Hartmut about it on IRC.
 My solution to the implementation defined behavior that makes all fusion
 sequence operations have an unpredictable execution ordering. My solution
 was to create my own version of fusion::as_list that has a guaranteed
 execution order. The key being to make copies of the sequence values in
 the correct ordering. Which boils down to changing
 fusion::detail::build_cons<First,Last,false>::call(...) from:

 {{{
 static type
 call(First const& f, Last const& l)
 {
     return type(*f, next_build_cons::call(fusion::next(f), l));
 }
 }}}

 To:

 {{{
 static type
 call(First const& f, Last const& l)
 {
     typename result_of::value_of<First>::type v = *f;
     return type(v, next_build_cons::call(fusion::next(f), l));
 }
 }}}

-- 
Ticket URL: <https://svn.boost.org/trac/boost/ticket/2823#comment:4>
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