From: Bharat Ruparel <bruparel@...>
Date: 2008-03-04T07:00:56+09:00
Subject: Question on the Ruby Programming Language Book

I have been reading The Ruby Programming Language book by David Flanagan
and Matz.  It is written quite well.  Some examples are not clear (to
me):  Here is one from Chapter 7 page 244 which defines a class to set
enumerated types:

class Season
  NAMES = %w{ Spring Summer Autumn Winter }  # Array of season names
  INSTANCES = []                             # Array of Season objects

  def initialize(n)  # The state of a season is just its
    @n = n           # index in the NAMES and INSTANCES arrays
  end

  def to_s           # Return the name of a season
    NAMES[@n]
  end

  # This code creates instances of this class to represent the seasons
  # and defines constants to refer to those instances.
  # Note that we must do this after initialize is defined.
  NAMES.each_with_index do |name,index|
    instance = new(index)         # Create a new instance
    INSTANCES[index] = instance   # Save it in an array of instances
    const_set name, instance      # Define a constant to refer to it
  end

  # Now that we have created all the instances we'll ever need, we must
  # prevent any other instances from being created
  private_class_method :new,:allocate  # Make the factory methods
private
  private :dup, :clone                 # Make copying methods private
end

My question is how do you use this class from the client code?  Can
someone give some examples?

Thanks.

Bharat
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