From: "David A. Black" <dblack@...>
Date: 2008-09-09T07:32:34+09:00
Subject: Re: "Pointer" to an object? (i.e. reflect changes to origina

Hi --

On Tue, 9 Sep 2008, Doug Glidden wrote:

> Calamitas wrote:
> [snip]
>> Or closer to the pointer solution you want:
>>
>>   p.primary_email = lambda { p.personal_email }
>>   p.personal_email = 'me@gmail.com'
>>   puts p.primary_email.call
>>
>> The lambda expression corresponds to the address operator, the .call
>> corresponds to a pointer dereference.
>>
>> Peter
>
> Peter,
>
> Thanks!  I had just (literally within the last ten minutes) thought of
> the possibility of using an enclosure of some sort to do the trick.  I
> was playing around with using a proc, you used a lambda, I think either
> one will probably work with some tweaking.  This is the "perfect"
> solution, I think.
>
> I'm a little curious how this will react if p.primary_email.call is
> executed when p is not in scope, e.g. if something like the following
> occurs, so I'm going to play around:
>
>  def do_something(person)
>    email = person.primary_email.call
>    # do more stuff...
>  end
>
>  p = Person.new
>  p.personal_email = 'me@home.com'
>  p.primary_email = lambda {p.personal_email}
>  do_something p
>
> Will the lambda be able to handle that situation?  Like I said, I'm
> going to play around with it.

Yes; the lambda carries its local scope with it, so wherever it's
called, it will have access to the p that it started with.


David

-- 
Rails training from David A. Black and Ruby Power and Light:
   Intro to Ruby on Rails  January 12-15   Fort Lauderdale, FL
   Advancing with Rails    January 19-22   Fort Lauderdale, FL *
   * Co-taught with Patrick Ewing!
See http://www.rubypal.com for details and updates!