Module to facility the enumeration of constants

enumerable_constants.rb

# This module should be used for situations where enumerating over constant values is desired.
# This facilitates keeping the code DRY by keeping the constant values defined in one place, and 
# still having the ability to enumerate over them wherever they are needed.
#
# Example use cases:
#
# * defining constants for possible field values in an AR object and including this module to 
#   provide access to the values in a 'validates_inclusion_of' validation
# * defining constants for select box values in a view and including this module to allow them to be
#   enumerated over in the select tag

module EnumerableConstants

  def EnumerableConstants.included(mod)
    class << mod
      include Enumerable
      
      def enumerable(*consts)
        @enumerable_consts = consts unless consts.empty?
      end
      
      # Yields each constant value to &block.  By default, all constants defined by the
      # including class are yielded.  If specific constants are to be yielded, call 
      # EnumerableConstants#enumerable(*consts) before calling this method.
      
      def each(&block)
        consts = @enumerable_consts || self.constants.grep(/[^a-z][A-Z_]+/)
        consts.each do |const|
          yield self.const_get(const)
        end
      end

      # #each_constant is provided as syntactic sugar for situations where it may be more appropriate than #each
      alias_method :each_constant, :each
    end
  end 
end

enumerate_all_constants.rb

class Program

  def do_stuff
  end

  class Statuses
    include EnumerableConstants

    PENDING = 'pending'
    RUNNING = 'running'
    DONE = 'done'
  end
end

Program::Statuses::DONE
#=> "done"

Program::Statuses.collect
#=> ["pending", "done", "running"]

enumerate_specific_constants.rb

class Program
  include EnumerableConstants
  enumerable :PENDING, :RUNNING, :DONE

  PENDING = 'pending'
  RUNNING = 'running'
  DONE = 'done'
  CONST_WE_DONT_WANT_EXPOSED_IN_ITERATION = 'not in iterate'

  def do_stuff
  end
end

Program::CONST_WE_DONT_WANT_EXPOSED_IN_ITERATION
#=> "not in iterate"

Program.each_constant{|c| puts c}
#=> pending
#=> running
#=> done