title: How to check presence of static const member with SFINAE
body: <p>Suppose i have several structs with fields that are optional:</p>
  
  <pre><code>struct Param1
  {
      static const bool x = true;
  };
  
  struct Param2
  {
  };
  </code></pre>
  
  <p>And want to write template function</p>
  
  <pre><code>template &lt;class ParamType&gt;
  bool ReturnParam();
  </code></pre>
  
  <p>Which should return <code>ParamType::x</code> if static field <code>x</code> exists, otherwise it should return <code>false</code></p>
  
  <p>I suppose that some SFINAE magic should help.</p>
  
  <h3>Constraint</h3>
  
  <p>I am using MSVC 2010, so I cannot use most of C++11 features.</p>