From: sur max <sur.max@...>
Date: 2007-02-16T22:09:29+09:00
Subject: Re: class design issues

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attr_reader i mean !!

On 2/16/07, sur max <sur.max@gmail.com> wrote:
>
> I think just declaring it as attr_accessor is not that much a protection
> !!
>
> its fine that
>
> lf1.name  # => error, undefined method `name=' f
>
> BUT, it can easily be broken as....
>
> lf1.instance_variable_set("@name", "new broken name")
>
> lf1.name  # => "new broken name"
>
>
>
>
> On 2/16/07, Robert Klemme <shortcutter@googlemail.com> wrote:
> >
> > On 16.02.2007 13:51, Spitfire wrote:
> > >   I have a class which takes an input and produces an object. Let's
> > say,
> > > it takes inputs about specifications of a life-form, and then creates
> > it
> > > (instantiates say an object, 'LifeForm'). Let's call this factory
> > class
> > > 'Creator'. Now, my problem is how do I ensure that once 'Creator'
> > > returns a 'LifeForm', any external/requestor class can only view the
> > > properties of LifeForm, that were set during creation, and not be able
> >
> > > to modify them???
> > >   How do I design these imaginary classes 'Creator' and 'LifeForm'?
> >
> > First, it is very hard to actually prevent changes of instance variables
> > (if it is possible at all).  For your purposes it is probably sufficient
> >
> > to define attribute readers only.  Second, you do not necessarily need a
> > second class - basically LifeForm is the factory for LifeForm instances.
> >   So you could do
> >
> > class LifeForm
> >    attr_reader :age, :name, :foo
> >
> >    def initialize(age,name,foo)
> >      @age = age
> >      @name = name
> >      @foo = foo
> >    end
> > end
> >
> > irb(main):010:0> lf1 = LifeForm.new 10, "bla", "buzz"
> > => #<LifeForm:0x7ef6f5e4 @name="bla", @foo="buzz", @age=10>
> > irb(main):011:0> lf1.name
> > => "bla"
> > irb(main):012:0> lf1.name = "ddd"
> > NoMethodError: undefined method `name=' for #<LifeForm:0x7ef6f5e4
> > @name="bla", @foo="buzz", @age=10>
> >          from (irb):12
> >          from :0
> >
> > HTH
> >
> >         robert
> >
> >
>
>
> --
> sur
> http://expressica.com




-- 
sur
http://expressica.com

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