[Boost-bugs] [Boost C++ Libraries] #5664: multi_array's operator() checks for Collection concept but requires RandomAccessCollection

Subject: [Boost-bugs] [Boost C++ Libraries] #5664: multi_array's operator() checks for Collection concept but requires RandomAccessCollection
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2011-06-30 20:23:04

#5664: multi_array's operator() checks for Collection concept but requires
RandomAccessCollection
------------------------------------+---------------------------------------
 Reporter:  matthias_berndt@…       |       Owner:  garcia     
     Type:  Bugs                    |      Status:  new        
Milestone:  To Be Determined        |   Component:  multi_array
  Version:  Boost 1.46.1            |    Severity:  Problem    
 Keywords:                          |  
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 Hi,

 The summary says it all, really. The code that implements operator() looks
 like this:

 {{{
   template <typename Reference, typename IndexList, typename TPtr>
   Reference access_element(boost::type<Reference>,
                            const IndexList& indices,
                            TPtr base,
                            const size_type* extents,
                            const index* strides,
                            const index* index_bases) const {

     ignore_unused_variable_warning(index_bases);
     ignore_unused_variable_warning(extents);
 #if !defined(NDEBUG) && !defined(BOOST_DISABLE_ASSERTS)
     for (size_type i = 0; i != NumDims; ++i) {
       BOOST_ASSERT(indices[i] - index_bases[i] >= 0);
       BOOST_ASSERT(size_type(indices[i] - index_bases[i]) < extents[i]);
     }
 #endif

     index offset = 0;
     for (size_type n = 0; n != NumDims; ++n)
       offset += indices[n] * strides[n];

     return base[offset];
   }
 }}}

 It uses operator[] for the indices, but that operator is not a member of
 the Collection concept, so an iterator should be used instead.

 I also think that requiring an index type to model the Collection concept
 was a poor choice. size(), empty() and swap() aren't needed to subscript a
 multi_array. Also, begin() and end() are required to be member functions,
 which is hard to do when trying to use a type from a library. I think it
 would be better to require a SinglePassRange, as it solves the above
 problems.

-- 
Ticket URL: <https://svn.boost.org/trac/boost/ticket/5664>
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