title: Make a class that cannot be instantiated?
body: <p>Suppose that I have a class <code>Bar</code>. I want to use <code>Bar</code> uniquely as a base class, e.g.:</p>
  
  <pre><code>class Foo : public Bar
  </code></pre>
  
  <p>I want to disallow <code>Bar</code> from being able to be instantiated. In other words, I want <code>Bar object;</code> to be an error. Is this possible to do?</p>