Re: [Boost-bugs] [Boost C++ Libraries] #3982: mpl::at documentation out of sync with code

Subject: Re: [Boost-bugs] [Boost C++ Libraries] #3982: mpl::at documentation out of sync with code
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2010-05-17 09:33:44

#3982: mpl::at documentation out of sync with code
---------------------------------------------+------------------------------
 Reporter:  manfred.doudar@…                 |       Owner:  agurtovoy
     Type:  Bugs                             |      Status:  new      
Milestone:  Boost 1.43.0                     |   Component:  mpl      
  Version:  Boost 1.42.0                     |    Severity:  Problem  
 Keywords:  mpl::at default                  |  
---------------------------------------------+------------------------------

Comment(by dsaritz@…):

 In my experience (with MSVC++) implementing the defaulted at as

 ...

 {
   typedef typename boost::mpl::at<Seq, Key>::type in_seq;

   typedef typename boost::mpl::if_
         <
             boost::is_same<in_seq, boost::mpl::void_>,
             Default,
             in_seq
         >::type type;
 }

 or by using find + compare-to-end (instead of void) + deref proved to be
 more (compile-time) efficient (probably because of skipping the
 instantiation of has_key<>...)...

 In any case, the defaulted at should IMO be provided out-of-the-box by MPL
 (both because of 'cleanness' and because the library author has the best
 chance to make it as efficient as possible)...

-- 
Ticket URL: <https://svn.boost.org/trac/boost/ticket/3982#comment:2>
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