title: Same instance variable for all actions of a controller
body: <p>I have a rails controller with two actions defined: <code>index</code> and <code>show</code>.
  I have an instance variable defined in <code>index</code> action. The code is something like below:</p>
  
  <pre><code>def index
    @some_instance_variable = foo
  end
  
  def show
    # some code
  end
  </code></pre>
  
  <p>How can I access the <code>@some_instance_variable</code> in <code>show.html.erb</code> template?</p>