From: John W Higgins <wishdev@...>
Date: 2010-10-21T03:29:18+09:00
Subject: Re: [Q] best practice for redefining methods at runtime?

--0016362840728d54a004931094a3
Content-Type: text/plain; charset=ISO-8859-1

Morning Chuck.

On Wed, Oct 20, 2010 at 8:31 AM, Chuck Remes <cremes.devlist@mac.com> wrote:

> I have a class that I would like to "freeze" when it reaches a particular
> state so that it becomes read-only. I do *not* want to use the existing
> #freeze method because it raises an exception when there is an attempted
> mutation on a frozen object and I want the attempt to be silent. It appears
> that the best way to enforce this (state machine pattern) is by redefining
> the accessors and other methods that cause mutations to be no ops.
>
> What is the preferred practice for doing that?
>
>
You could in the alternative have the ops that mutate do an "unless" at the
top of the method to bake the freeze into the method as opposed to
redefining

Using your example


class Foo
 attr_accessor :frozen
 attr_reader :bar, :baz, :quxxo

 def bar= new_bar
   unless @frozen @bar = new_bar
 end

 def baz= new_baz
   unless @frozen @baz = new_baz
 end

 def quzzo= new_quzzo
   unless @frozen @quzzo = new_quzzo
 end
end

It's a little more work and a slight amount of overhead for the unless
check. But it does eliminate the need to redefine your methods. It also very
clearly spells out what you are freezing.

John

--0016362840728d54a004931094a3--