From: "Jesús Gabriel y Galán" <jgabrielygalan@...>
Date: 2009-02-09T04:31:18+09:00
Subject: Re: best way to protect class instance variables

On Sun, Feb 8, 2009 at 8:11 PM, Barun Singh <barunio@gmail.com> wrote:
> Suppose I generate a class instance variable and create an accessor
> function for it as follows:
>
> class MyClass
>  @blah = [0,1]
>  def self.blah
>    @blah
>  end
> end
>
> I would like to prevent any other piece of code from having any way of
> changing the value of the class variable.  While the code above prevents
> me from saying "MyClass.blah = 'hello'", it does allow me to say
> "MyClass.blah[0] = 'hello'", which changes the value of the class
> instance variable (to ['hello',1]) any time I try to access it in the
> future.

You could freeze it:


irb(main):009:0> class Blah
irb(main):010:1> @blah = [0,1].freeze
irb(main):011:1> def self.blah
irb(main):012:2> @blah
irb(main):013:2> end
irb(main):014:1> end
=> nil
irb(main):015:0> Blah.blah
=> [0, 1]
irb(main):016:0> Blah.blah[0] = "hello"
TypeError: can't modify frozen array
	from (irb):16:in `[]='
	from (irb):16


This could save you from accidental changes, but somebody could always
do this and trash your frozen array:

irb(main):017:0> class Blah
irb(main):018:1> @blah = %w{nothing is really safe}
irb(main):019:1> end
=> ["nothing", "is", "really", "safe"]
irb(main):020:0> Blah.blah
=> ["nothing", "is", "really", "safe"]

or this:

irb(main):021:0> Blah.send (:instance_variable_set, "@blah", [1,2,3])
(irb):21: warning: don't put space before argument parentheses
=> [1, 2, 3]
irb(main):022:0> Blah.blah
=> [1, 2, 3]

or probably many other things to achieve that. So it's not really safe.

Jesus.