From: James French <James.French@...>
Date: 2009-11-07T00:57:42+09:00
Subject: Re: encapsulation issue



> -----Original Message-----
> From: David A. Black [mailto:dblack@rubypal.com]
> Sent: 06 November 2009 14:01
> To: ruby-talk ML
> Subject: Re: encapsulation issue
> 
> Hi --
> 
> On Fri, 6 Nov 2009, James French wrote:
> 
> > Hi,
> >
> > Is there any way of providing read only access to an array? (problem
> shown by code below).
> >
> > class A
> >
> >  def initialize
> >    @dependencies = []
> >  end
> >
> >  # intended to be read only access
> >  def dependencies
> >    @dependencies
> >  end
> >
> >  def addDependency(d)
> >    @dependencies << d
> >    puts "adding #{d}"
> >  end
> > end
> >
> >
> > a = A.new
> > a.addDependency("foo")
> > a.dependencies << "bar" # encapsulation subverted
> >
> > puts a.dependencies   # foo and bar both in array
> 
> You can freeze the array:
> 
>    a = [].freeze
>    a << 1          # TypeError: can't modify frozen array
> 
> 
> David
> 
> --
> The          Ruby training with D. Black, G. Brown, J.McAnally
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> Rubyist      http://www.thecompleatrubyist.com
> 
> David A. Black/Ruby Power and Light, LLC (http://www.rubypal.com)

But then I can't legitimately push to it in addDependency...