Is "proc" required with conditional before_action/before_filter?

Behold, a before_filter:

class ThingController < ApplicationController
  before_filter :check_stuff, :if => proc {Rails.env.production?}
end

During a recent code review, I was asked, "Is the proc is required for this to work?" The answer appears to be 'yes', but it's a reasonable question, and I had intended to answer it by referring to the Rails docs or guides or something on the use of conditionals with before_filter (now an alias of before_action).

I couldn't find any. The Action Controller Guide mentions :only/:except, but not :if/:unless.

Failing that, is there somewhere in the code I can point to that covers this? It's mentioned briefly here, but that's more about how :only and :except are handled, rather than :if or :unless.

Found it on Rails Guides: http://guides.rubyonrails.org/active_record_callbacks.html#conditional-callbacks

Turns out a Proc isn't always required for it to work.

the :if and :unless options, which can take a symbol, a string, a Proc or an Array.

So in your case you could probably get away with

before_action :check_stuff, if: "Rails.env.production?"

Finding things in Rails documentation can be a pain sometimes, but at least questions like this make things easier to find over time since StackOverflow is well indexed and has high search rankings.