From: Jim Freeze <jfreeze@...>
Date: 2002-01-17T04:09:34+09:00
Subject: Re: Protecting a member hash

On Thu, Jan 17, 2002 at 03:55:38AM +0900, Phil Tomson wrote:
> In article <20020116131656.A93722@freebsdportal.com>,
> Jim Freeze  <jfreeze@freebsdportal.com> wrote:
> >Hi:
> >
> >I have a class that stores data in a hash.
> >I would like the user to be able to retrieve
> >values from the hash, but not modify it.
> >
> >class Test
> >  attr_reader :entity
> >  def initialize
> >    @entity = {'a'=>"fred"}
> >  end
> >end
> >
> >t = Test.new
> >p t.entity   #=> {"a"=>"fred"}
> >t.entity['a'] = "changed"
> >p t.entity   #-> {"a"=>"changed"}
> >
> >
> >Other than freezing @entity, is it possible
> >top protect it from being changed?
> >
> 
> Why not just define a '[]' method, but not a '[]=' method in your class 
> and don't use the attr_reader.  Like:
> 
> class Test
>   def initialize
>     #HasA hash:
>     @entity = {'a'=>"fred"}
>   end
> 
>   def [](key)
>     @entity[key]
>   end
> 
> end
> 
> t = Test.new
> p t['a']       #this will work
> t['b']="Error" #this will raise an error
> 
> So basically, you're hiding the hash from the outside world.

Well. that would work, but the real story is that I have
multiple hashes in the class. So, the single Test#[] is
limiting. I suppose I would write a class for each hash.
Is there a cheaper way?

Jim

> 
> Phil
> 

-- 
Jim Freeze
Today is a fine day for Ruby programming.
www.freeze.org