title: boost filtering streambuf unable to initialise stream
body: <p>I am tring to decompress a bz2 file like so:</p>
  
  <pre><code>#include &lt;boost/iostreams/filter/bzip2.hpp&gt;
  #include &lt;boost/iostreams/filtering_streambuf.hpp&gt;
  ifstream file (file_name);
  boost::iostreams::filtering_streambuf&lt;boost::iostreams::input&gt; in;
  in.push(boost::iostreams::bzip2_decompressor());
  in.push(file);
  
  std::ifstream input(&amp;in);
  </code></pre>
  
  <p>but execution fails with the messages:</p>
  
  <pre><code>error: no matching constructor for initialization of 'std::ifstream' (aka 'basic_ifstream&lt;char&gt;')
  std::ifstream input(&amp;in);
                ^     ~~~
  /Library/Developer/CommandLineTools/usr/bin/../include/c++/v1/iosfwd:131:33: note: candidate constructor (the implicit copy constructor) not viable: no known conversion from 'boost::iostreams::filtering_streambuf&lt;boost::iostreams::input&gt; *' to 'const std::__1::basic_ifstream&lt;char, std::__1::char_traits&lt;char&gt; &gt;' for 1st argument
  class _LIBCPP_TYPE_VIS_ONLY basic_ifstream;
                              ^
  </code></pre>
  
  <p>I am not sure what I am doing wrong here. This is the recommended procedure according to <a href="http://www.boost.org/doc/libs/1_49_0/libs/iostreams/doc/tutorial/writing_devices.html" rel="nofollow">http://www.boost.org/doc/libs/1_49_0/libs/iostreams/doc/tutorial/writing_devices.html</a></p>