title: Casting between two types derived from the (same) interface
body: <p>I have an interface and two types that derive from it.</p>
  
  <p>However, I cannot do the following:</p>
  
  <pre><code>B objectB = (B) objectA
  </code></pre>
  
  <p>Where B derives from Interface1 (I am making up the name of classes but the point still stands), and likewise for objectA (which is of type A). I get the following error message:</p>
  
  <blockquote>
    <p>Cannot cast expression of type A to B. </p>
  </blockquote>
  
  <p>Both types are deriving from the interface, what am I missing?</p>