title: Why use Proc.new to call a method in a Rails callback?
body: <p>in all the tutorials for RoR I see instances where the coder chose to use Proc.new when seemingly it is both unnecessary and rather unattractive.</p>
  
  <p>Example, here is a callback for placed in a model, one using Proc.new the other presumably doing the same thing:</p>
  
  <pre><code>class Order &lt; ActiveRecord::Base  
    before_save :normalize_card_number,  
      :if =&gt; Proc.new { |order| order.paid_with_card? }  
  end
  
  class Order &lt; ActiveRecord::Base
    before_save :normalize_card_number, :if =&gt; "paid_with_card?"
  end
  </code></pre>
  
  <p>So what's the difference? Why use the Proc? Don't they both call the "paid_with_card?" method?</p>
  
  <p>Thanks in advance</p>