title: Forward Declaration of class in C++, incomplete type
body: <p>I have an issue with Forward Declaration in C++ using clang compiler. Here is my code. It points data in CReference member as incomplete type.
  Please Help</p>
  
  <pre><code>class Internal;
  
  class CReference {
  private:
      Internal data;
  public:
  
      CReference () {}    
      ~CReference (){}
  };
  
  class Internal {
  public:
      Internal () {}
      ~Internal () {}
  };
  </code></pre>