title: assign to base component of a derived class
body: <p>How can i assign a base class instance to the base class "member" of a derived class from the derived class?</p>
  
  <pre><code>class A{
  public:
     A();
     A(const A&amp; i);
     A &amp;operator =(const A&amp; i);
     ~A();
  };
  
  class B: public A{
  public:
    void f(){
      A a;
      // calc(a);
      *this = a; // &lt;- how?
    }
    void x(){};
  private:
    int i;
  };
  </code></pre>