gistfile1.rhtml

<%= options_from_collection_for_select(@product.sizes, :name, :id, :disabled => lambda{|size| size.out_of_stock?}) %>

<!-- If small and medium returned true for the method out_of_stock?, you’d get something like: -->

<option value=“23“ disabled=“disabled“>small</option>
<option value=“24“ disabled=“disabled“>medium</option>
<option value=“25“>large</option>
<option value=“26“>extra large</option>