Sometimes you want enumerable style uniqueness in class constants. This raises an error if two constants are defined with the same value.

uniq_constants.rb

class DuplicateConstantError < StandardError; end

module UniqConstants
  def uniq_constants!
    values = constants.group_by { |c| const_get(c) }
    dupes = values.values.select { |a| a.length > 1 }
    raise DuplicateConstantError, "Duplicate constants defined : #{dupes.flatten.inspect}" if dupes.present?
  end
end

# Example :
#
# class Event
#   CONSTANT_ONE = 1
#   CONSTANT_TWO = 2
#   DUPLICATE_CONSTANT = 2
#   uniq_constants!
# end