Re: [Boost-bugs] [Boost C++ Libraries] #6126: Signed integer members of Boost.Fusion adapted ADTs are not output correctly with Boost.Spirit.Karma rules

Subject: Re: [Boost-bugs] [Boost C++ Libraries] #6126: Signed integer members of Boost.Fusion adapted ADTs are not output correctly with Boost.Spirit.Karma rules
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2012-02-02 01:03:20

#6126: Signed integer members of Boost.Fusion adapted ADTs are not output
correctly with Boost.Spirit.Karma rules
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  Reporter:  t0rt1e@…          |       Owner:  hkaiser                                                                                                             
      Type:  Bugs              |      Status:  new                                                                                                                 
 Milestone:  To Be Determined  |   Component:  spirit                                                                                                              
   Version:  Boost 1.48.0      |    Severity:  Regression                                                                                                          
Resolution:                    |    Keywords:  patch proposed, Boost.Spirit.Karma, Boost.Fusion, BOOST_FUSION_ADAPT_CLASS, BOOST_FUSION_ADAPT_ADT, short, int, long
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Comment (by bugs@…):

 Thinking aloud:

 I suppose the extract_from helper should just return the attribute proxy
 by value.

 I can see how that is undesirable for the general case (non-copyable or
 copy-expensive attributes), but keep in mind that for adapted ADT's, the
 `adt_attribute_proxy` instance can easily be returned by value while still
 allowing the compiler to generate optimum code:

   - RVO elides the copying,
   - the caller can bind the temporary to a const& in case it needs to
 access it twice (insert_int) and
   - inlining does the rest

 ----

 Of the wall: might this (the 'premature' decaying of the proxy to it's
 exposed attribute type) have something to do with the special casing of
 single-element-sequences in attribute extraction (decaying of a sequence
 to it's single element)?

-- 
Ticket URL: <https://svn.boost.org/trac/boost/ticket/6126#comment:14>
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