From: Eye Matz <matz@...>
Date: 2006-10-03T23:50:12+09:00
Subject: Re: Newbie: Question => How to do this with Classes ?

unknown wrote:
> So, you could do this:
> 
>    class Important
>      def self.set_this_value_method(value)  # note the 'self'
>      end
>    end
> 
>    class SemiImportant < Important
>      set_this_value_method :x
>    end

Hi David,

Thanks for your reply!  This was very much the way I was trying to do 
things and expecting things to work, but when I did it, things did NOT 
work. Go figure! :(  Having taken yours & Jean's replies, I came up with 
this heavily commented code, WITH lots of questions inside the comments 
:)

==============

# base class that is extended by other classes for shared 
methods/variables within the
# instance object
class Important
  # Not sure if this is really needed, or how to refer/change this to a 
@@class_variable ??
  attr_accessor :my_value

  # the method that will be used in sub-classes to set the internal 
value
  def self.set_this_value_method(value)  # note the 'self'
    # commented out use of class variable, since using a method is 
better for
    # possible expansion in the future
    #@@my_value = value
    # call to internal method that sets the value to the class variable
    self.set_my_value(value)
  end

  # method that sets/(process) the actuall value
  def self.set_my_value(value)
    # using class variable here, but don't understand fully WHY?
    # should ideally be normal instance variable, but don't know how
    @@my_value = value
    # why does not this type of syntax work ?
    #self.my_value = value
  end

  # just dumps the value out
  def get_my_value
    @@my_value
  end

  def the_value
    # using the method instead of the variable here
    "the_value: my value is [#{get_my_value}]"
  end
end

# sub-class that is based upon base class
class SemiImportant < Important
  # here we set the internal 'my_value' variable to something
  set_this_value_method 'something'
end

# creating a new instance
sc = SemiImportant.new
# why does this NOT show the my_value variable?
# how could I make it show this variable?
puts sc.inspect	# => #<SemiImportant:0x35409c>

puts sc.get_my_value # => something
puts sc.the_value  # => the_value: my value is [something]
puts sc.my_value  # => nil
# with this call I can change the value of my_value
sc.class.superclass.set_my_value("Don't understand fully")
# but I cannot retrieve the value set with this call. WHY??
puts sc.class.superclass.my_value

==========

Hopefully someone else that is struggling with the same can find this 
little snippet and hopefully save themselves some over-worked brain 
cells.

If you (anyone) can answer the included questions I'd love to know the 
answers.

Thanks again.

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