title: What is the effect of the pipe operator in c++ boost::adaptors::filtered?
body: <p>In <a href="https://www.boost.org/doc/libs/1_49_0/libs/range/doc/html/range/reference/adaptors/reference/filtered.html" rel="noreferrer"><code>boost::adaptors::filtered</code></a> the filter function is used likeso:</p>
  
  <pre><code>std::vector&lt;int&gt; input;
  input += 1,2,3,4,5,6,7,8,9;
  
  boost::copy(
          input | filtered(is_even()),
          std::ostream_iterator&lt;int&gt;(std::cout, ","));
  </code></pre>
  
  <p>What is the effect of the pipe operator in this case? It is not defined for <code>std::vector</code>, is it an overload? If so, how does one effectively search for such operators in libraires like boost?</p>