Class factory mixin
<p>I would like to create in a mixin <code>class</code> that would impart a <code>class</code> factory method for the final class of a concrete type through several layers of inheritance. More specifically, I would like to have the factory method produce a new instance of the actual object it is called as a member of.</p>

<p>So, class "factory" is inherited by class <code>A</code>, class <code>A</code> is inherited by class <code>B</code>, I would like to find a way to do <code>B::create()</code> and create an instance of <code>B</code>. As far as I can tell this precludes the use of a template taking the type in the class <code>A</code> since then <code>B::create()</code> would produce an instance of <code>A</code>.</p>
