merge_html_attr.rb

class Hash
 
  def merge_html_attr!(other)
    merged = self.merge(other) do |key, a, b|
      if key == :class && a.is_a?(String) && b.is_a?(String)
        [a, b].join(' ')
      else
        b
      end
    end
    replace(merged)
  end
 
  def merge_html_attr(other)
    dup.merge_html_attr!(other)
  end
 
end