title: Get child class of argument
body: <p>I have a method which gets a parent class as an argument.
  I need to know at compile time what is the child class of that argument.</p>
  
  <pre><code>class A{
  ...
  };
  
  class B: public A{
  ...
  };
  
  class C: public A{
  ...
  };
  
  void foo(A a){
      //is a specialized in B or C?
  }
  
  C c;
  foo(c); //here it is C
  </code></pre>