title: codeigniter instance of model class
body: <p>I'm developing a site with codeigniter. Now, normally when you use a class in codeigniter, you basically use it as if it were a static class. For example, if I head a model called 'user', I would first load it using</p>
  
  <pre><code>$this-&gt;load-&gt;model('user');
  </code></pre>
  
  <p>and than, I could invoke methods on that user class like </p>
  
  <pre><code>$this-&gt;user-&gt;make_sandwitch('cheese');
  </code></pre>
  
  <p>in the application that I'm building, I would like to have one UserManagement class, which uses a class called 'user'.</p>
  
  <p>so that, for example I could </p>
  
  <pre><code>$this-&gt;usermanager-&gt;by_id(3);
  </code></pre>
  
  <p>and this would return an <strong>instance</strong> of the user model where the id is 3.
  What's the best way to do that?</p>