title: Appending two casted class lists together
body: <p>I have a <code>Cat</code> class and a <code>Dog</code> class that implement an interface called <code>IAnimal</code>. </p>
  
  <p>I have a method that fetches a list of <code>cats</code> and <code>dogs</code>. 
  Currently I can cast the <code>cats</code> to an <code>IAnimal</code> and add it to the <code>animalList</code>. </p>
  
  <pre><code>List&lt;IAnimal&gt; animalList;
  
  ...
  
  public void setUpList(List&lt;Cat&gt; cats, List&lt;Dog&gt; dogs){
     animalList = cats.ToList&lt;IAnimal&gt;();
  }
  </code></pre>
  
  <p>Is there an eloquent way to cast both the <code>cats</code> and <code>dogs</code> to an <code>IAnimal</code> and combine them to a list?</p>