From: Rich Kilmer <rich@...>
Date: 2001-10-07T03:41:06+09:00
Subject: [ruby-talk:22164] Creating external accessors for class constants

I find myself wanting to use class constants more globally in my code.  Because of Ruby's encapsulation rules, every attribute (and constant) is private.  A helper method exists on Module to simplify externalizing attributes:

attr, attr_accessor, attr_reader, attr_writer

I was wondering whether it would make sense to have a similar method for class constants?

const_reader

defined as follows....

# add the const_reader method to Module
class Module
  def const_reader(*symbols)
    symbols.each do |symbol| 
      class_eval "def #{self.name}.#{symbol.to_s}; #{symbol.to_s}; end"
    end
  end
end

# define constants and export them via const_reader:
class Airlines
  AA="American Airlines"
  BA="British Airways"
  const_reader :AA, :BA
end

# These constants are now accessible via class methods (publicly)
# but (still) as constants internal to the class (no method overhead).

puts Airlines.AA # => "American Airlines"
puts Airlines.BA # => "British Airways"

-Rich Kilmer