title: Use of "using" in header files
body: <p>I understood, that I should not use this in a header file:</p>
  
  <pre><code>using namespace foo;
  </code></pre>
  
  <p>Because it brings the namespace foo in the global scope for anyone who uses my header file.</p>
  
  <p>Can I prevent this from happening, if I do it in my own namespace? For example like this:</p>
  
  <pre><code>namespace my_lib
  {
      using namespace foo;
  
      // my stuff
      // ...
  }
  </code></pre>
  
  <p>Now the using namespace foo should be restricted to the scope of the namespace my_lib, right?</p>