title: How important is consistent usage of using declarations?
body: <p>Most of the research I've done on the use of using declarations, including reading relevant sections of various style guides, indicates that whether or not to use using declarations in C++ source files, as long as they appear after all #includes, is a decision left to the coder. Even the style guides I read, which usually come down on one side or the other of such common disputes for the sake of consistency, are fairly flexible in this regard.</p>
  
  <p>My question is, given this high degree of flexibility, how important is it to use a consistent style? For example, suppose an author wrote something like</p>
  
  <pre><code>using std::vector;
  
  vector&lt;T&gt; v;
  
  std::cout &lt;&lt; v[0] &lt;&lt; std::endl;
  </code></pre>
  
  <p>Is the inconsistent application of using on std::vector but not std::cout or std::endl generally considered acceptable, or would it be considered undisciplined?</p>