From: Ohad Lutzky <lutzky@...>
Date: 2006-09-05T18:24:26+09:00
Subject: Enum

I want an enum of sorts in my Rails application.

I have a Project object, which has four possible status settings, as 
indicated here:

  class Project < ActiveRecord:Base
    ...
    class << self
      def statuses
        [ 'Hidden', 'Available', 'In progress', 'Complete' ]
      end
    end
    ...
  end

These are not expected to change, so hardcoding is preferable. Of 
course, there is a 'status' column in the project table, so rails 
creates a 'status' accessor.

However, later in the code I will want to check the status myself. For 
example, 'Complete' projects won't be shown in the same place as 
'Available' ones, and 'In progress' and 'Hidden' projects won't be shown 
at all (not sure about In progress ATM though, so I want to keep it 
flexible). Now, it would be pretty ugly checking

  if a_project.status == 2 # Project is in progress

So one possibility is to add methods like

  class Project
    def in_progress?
      self.status == 2
    end
  end

Another interesting option is this:

  class Project
    def status_is?(_status)
      [ :hidden, :available, :in_progress, :complete ][self.status] == 
_status
    end
  end

If only I could count on hashes staying in order, a very pretty solution 
would
be:

  class Project
    class << self
      def statuses
        { :hidden => 'Hidden', :available => 'Available',
          :in_progress => 'In progress', :complete => 'Complete' }
        # Use Project.statuses.values for the dropdown
      end
    end
    def status_is?(_status)
      Project.statuses.keys[self.status] == _status
    end
  end

Unfortunately, "The order in which you traverse a hash by either key or 
value may seem arbitrary, and will generally not be in the insertion 
order." (ri).

Any other ideas for elegance?


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