Refactoring a HTML class collector?

Question

I have following HTML class collector. Is there a better way than []tap for this?

def tr_classes(user)
  classes = [].tap do |c|
    c << "error" if user.company.nil?
    c << "disabled" if user.disabled?
  end
  if classes.any?
    " class=\"#{classes.join(" ")}\""
  end
end

<tr<%= tr_classes(user) %>>
  <td><%= user.name %></td>
</tr>

Answer 1

Notes:

• This tap usage is not uncommon to see but IMHO it's very, very dubious. You can use a functional approach (see code below).
• I wouldn't return the string along with the attribute, just the array of classes (which Rails3 helpers understand).

I'd write:

def tr_classes(user)
  [
    ("error" if !user.company),
    ("disabled" if user.disabled?),
  ].compact.presence
end

Tables are usually easier to build from helpers. You now would use the function that way:

content_tag(:tr, :class => tr_classes(user)) do
  content_tag(:td, user.name)
end

Answer 2

What do you mean a "better way" than tap? Why are you using tap at all? Initialize an array. Conditionally append items to it. This pattern is as old as time, and there is no reason to shoe-horn in a Ruby-esque solution.

classes = [].tap do |c|
  c << "error" if user.company.nil?
  c << "disabled" if user.disabled?
end

vs

classes = []
classes << "error" if user.company.nil?
classes << "disabled" if user.disabled?

You've added so much complexity, both functionally and visually, for literally no gain. You've produced more and uglier code.