title: Namespace alias for subnamespaces in local scopes
body: <p>Consider that I want to call <code>boost::algorithm::join</code> as <code>boost::join</code>, but I don't want to import the subnamespace in the global namespace as:</p>
  
  <pre><code>namespace boost {
     using algorithm::boost;
  };
  </code></pre>
  
  <p>Because I want to call <code>boost::join</code> with that syntax only in a local scope of an specific function:</p>
  
  <pre><code>void my_fun()
  {
      namespace boost { // Doesn't allowed syntax in local scope
          using algorithm::join;
      }
  
      auto ret = boost::join(something...);
  }
  </code></pre>
  
  <p>A different approach would be:</p>
  
  <pre><code>void my_fun()
  {
     using boost::algorithm::join;
     auto ret = join(something...);
  }
  </code></pre>
  
  <p>But this would provoke a ADL lookup, and I don't want to do such a lookup, because I know what method I'm calling: <code>boost::algorithm::join</code>.</p>
  
  <p>Only, I'm trying to find the shorter <code>boost::join</code> way of calling it. What will be the correct syntax or idiom to create a "subnamespace" alias?</p>