Re: [Boost-bugs] [Boost C++ Libraries] #9742: for_each causes funny behavior in phoenix V3 expressions

Subject: Re: [Boost-bugs] [Boost C++ Libraries] #9742: for_each causes funny behavior in phoenix V3 expressions
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2014-04-02 19:59:58

#9742: for_each causes funny behavior in phoenix V3 expressions
-------------------------------+-----------------------------------
  Reporter:  Chromatix         |      Owner:  theller
      Type:  Bugs              |     Status:  new
 Milestone:  To Be Determined  |  Component:  phoenix
   Version:  Boost 1.54.0      |   Severity:  Problem
Resolution:                    |   Keywords:  phoenix,for_each,lazy
-------------------------------+-----------------------------------

Comment (by John Fletcher <J.P.Fletcher@…>):

 I think I now have a reason for this. The implementation of
 phoenix::for_each is located in
 {{{boost/phoenix/stl/algorithm/iteration.hpp}}}. The actual code is this:
 {{{
             template<class R, class F>
             F const operator()(R& r, F const& fn) const
             {
                 return std::for_each(detail::begin_(r), detail::end_(r),
 fn);
             }
 }}}
 The "C++ Standard Library" N.M.Josuttis p.300 explains the rationale for a
 return type from for_each. However in this case replacing the code by
 {{{
             template<class R, class F>
             F const operator()(R& r, F const& fn) const
             {
                 std::for_each(detail::begin_(r), detail::end_(r), fn);
             }
 }}}
 and making the return type void to code works. I think the return object
 is a temporary which is getting discarded and invalidating the return
 mechanism in the comma operator. I will discuss this with the other
 maintainers.

-- 
Ticket URL: <https://svn.boost.org/trac/boost/ticket/9742#comment:10>
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