DIY feature toggle to soft launch and dark launch features in Rails, based on Heroku config vars

dark_launch.rb

class DarkLaunch

  def self.feature_visible(feature_id, current_user)
  
    if !current_user
      # Only logged in users should have access to Dark Launch features
      return false
    end
    
    if Rails.env.development? || Rails.env.test?
      # On Dev and Test these features should always be visible (for now at least)
      return true
    end
    
    # We're prefixing the ENV var ourselves with 'FEATURE_'
    env_var = ENV["FEATURE_#{feature_id}"]
    
    if env_var
    
      # If it equals the string "PUBLIC" then return true and don't check invidiual user_ids anymore
      return true if env_var == "PUBLIC" 
        
      # If we've got an array then we'll check whether the user ID is in there
      # Note: this is the actual piece of logic that allows us to control who to launch a feature to. Right now we're basing this
      # off of customer IDs. This could as well be 10% of our users, traffic from a certain country, only users with an email
      # of ...@my_own_company.com or whatever.
      return env_var.split(',').include?(current_user.id.to_s) unless !env_var
    
    end
    
    # Apparently nothing succeeded before so let's be safe and return false for now
    false
    
  end
end

demo.haml

- if DarkLaunch.feature_visible('MY_NEW_FEATURE', current_user)
  .alert
    Hey, we're visible!
- else
  .alert
    There will be something visible soon here!

I would have expected env_var == "PUBLIC" to mean PUBLIC and thus enabling a feature even if the users isn't logged in, thus this would also work as a general switch not limited to dark launch ;)
This way you could also publicly launch a feature without a redeployment