title: How to get class instances in Ruby?
body: <p>Say I have a class called Post that has many initiated instances (i.e. <code>Post.new(:name =&gt; 'foo')</code>).</p>
  <p>Is there a way to retrieve all the instances of that class by calling something on it?
  I'm looking for something along the lines of <code>Post.instances.all</code></p>