Q:

C++11 compatibility of sparse matrix implementations

I try to create a compressed_matrix using a coordinate_matrix as a builder:
#include <boost/numeric/ublas/io.hpp>
#include <boost/numeric/ublas/matrix_sparse.hpp>

using namespace boost::numeric::ublas;

int main(int argc, char** argv) {
  coordinate_matrix<int> m1(100, 100, 100);

  for (int i = 0; i < 100; i++)
    m1.insert_element(i,i,i);

  compressed_matrix<int> m2(m1, 100);
}

This seems to work fine using boost 1.54 and clang, but when I compile it using std=c++11, an error is thrown:
 choeger@daishi /tmp % clang++ test.cpp --std=c++11
In file included from test.cpp:1:
In file included from /usr/include/boost/numeric/ublas/io.hpp:18:
In file included from /usr/bin/../lib/gcc/x86_64-redhat-linux/4.8.2/../../../../include/c++/4.8.2/sstream:38:
In file included from /usr/bin/../lib/gcc/x86_64-redhat-linux/4.8.2/../../../../include/c++/4.8.2/istream:38:
In file included from /usr/bin/../lib/gcc/x86_64-redhat-linux/4.8.2/../../../../include/c++/4.8.2/ios:40:
In file included from /usr/bin/../lib/gcc/x86_64-redhat-linux/4.8.2/../../../../include/c++/4.8.2/bits/char_traits.h:39:
/usr/bin/../lib/gcc/x86_64-redhat-linux/4.8.2/../../../../include/c++/4.8.2/bits/stl_algobase.h:147:7: error: no matching function for call to 'swap'
      swap(*__a, *__b);

Are there known incompatibilities of boost 1.54 with C++11? Or did I make some C++11 error? The 1.55 changelog does not mention ublas nor matrices, so I guess it is still present.
This happens both with gcc 4.8.2 and clang 3.4

A:

This is definitely a bug in Boost. The problem is that when BOOST_UBLAS_STRICT_MATRIX_SPARSE is defined, coordinate_matrix and its iterator types use a proxy class as their reference type:
#ifndef BOOST_UBLAS_STRICT_MATRIX_SPARSE
        typedef T &reference;
#else
        typedef sparse_matrix_element<self_type> reference;
#endif

which violates the C++ standard's requirement that the reference type for forward iterators is a true reference. C++11 [forward.iterators]/1 states: "A class or pointer type X satisfies the requirements of a forward iterator if ... if X is a mutable iterator, reference is a reference to T; if X is a const iterator, reference is a reference to const T, ...".
The coordinate_matrix iterators claim to be bidirectional iterators despite this fact, resulting in undefined behavior.

