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copied!<p>There are two immediate problems with your code:</p> <ul> <li><p>you compute <code>fusion::as_nview<N>(*it)</code> and try to store it as if it were a <code>fusion::result_of::as_nview<T::value_type, N>::type</code>; in truth it is a <code>fusion::result_of::as_nview<T::value_type const, N>::type</code> (<code>*it</code> has type <code>T::const_reference</code>); this is the source of your <code>const</code>-related errors.</p></li> <li><p>you try to accumulate the resulting views, but, as far I can tell from <a href="http://www.boost.org/doc/libs/1_52_0/libs/fusion/doc/html/fusion/view/nview.html" rel="nofollow">the Fusion docs</a>, valid operations on such a view are mostly those of a Fusion Random Access Sequence. In particular you can't add two views together, or default construct one. Here's a lead to a possible fix (by no means the only way though), not actually tested:</p> <pre><code>typedef typename Container::value_type view_type; typedef typename fusion::result_of::at_c<view_type, 0>::type reference; // boost::decay is from Boost.TypeTraits typedef typename boost::decay<reference>::type value_type; value_type zero = 0; return std::accumulate(container.begin(), container.end(), zero, add_views()); </code></pre> <p>where <code>add_views</code> is a functor that returns something in the spirit of <code>lhs + at<0>(rhs)</code>. Note that this solution only really makes sense if you intend for <code>c</code> to make views of length exactly one.</p></li> </ul>

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