From: Robert Klemme <shortcutter@...>
Date: 2012-02-17T19:57:37+09:00
Subject: Re: delete from class

On Fri, Feb 17, 2012 at 10:46 AM, Emil Enemærke <eme@medical-insight.com> wrote:
> Hi
>
> I have found this tutorial http://juixe.com/techknow/index.php/2007/01/22/ruby-class-tutorial/
>  where there is the following class:
>
> ###
> class Person
>  attr_accessor :fname, :lname
>
>  def initialize(fname, lname)
>    @fname = fname
>    @lname = lname
>  end
>
>  def to_s
>    @lname + ", " + @fname
>  end
>
>  def self.find_by_fname(fname)
>    found = nil
>    ObjectSpace.each_object(Person) { |o|
>    found.push(o) if o.fname == fname
>    }
>    found
>  end
> end
> ###

That's an awful and inefficient way to do it.  A proper implementation
would at least hold an Array or Hash with all Persons in some global
place instead of resorting to ObjectSpace.  ObjectSpace is a tool for
rather special situations and finalization handling.

> Is it possible to add a self.delete that will delete the entry found by the self.find_by_fname?

No.  What would "deleting" mean here?  There can be arbitrary many
references pointing to that instance found (including null, if GC has
not reclaimed an unreachable object):

~$ ruby19 -e 's="foo";id=s.object_id;s=nil;ObjectSpace.each_object(String){|st|
p st if st.object_id == id}'
"foo"

s is unreachable yet you see it through ObjectSpace.

Kind regards

robert

-- 
remember.guy do |as, often| as.you_can - without end
http://blog.rubybestpractices.com/