From: Charles Hixson <charleshixsn@...>
Date: 2003-11-15T01:56:37+09:00
Subject: Re: Singletons and Marshalling

That sure *looks* good.  It looks as if with only quite minor changes it 
will do exactly what I was hoping for.

Christoph wrote:

>------------
>/Christoph
>
>Please send off list mail to
>'my_mail@gmy.net'.gsub(/y/,'x') 
>
> 
>
>  
>
>>-----Original Message-----
>>From: Charles Hixson [mailto:charleshixsn@earthlink.net] 
>>Sent: Friday, 14 November, 2003 04:37 AM
>>To: ruby-talk ML
>>Subject: Singletons and Marshalling
>>
>>Does anyone know how singleton's and marshalling interact? Be dumped
>>
>>In particular, I want to have my singleton class be able to 
>>dump and load (and be saved on a file).  So I'm wondering if 
>>there are any methods to be implemented that would enable this.
>>
>>In particular, I'm composing a kind of container class that 
>>will contain 
>>either an array, a hash, or possibly both of values.   
>>Dumping it should 
>>be basically dumping all the members of the hash/array (plus 
>>a few more), and restoring should append the contents of the 
>>being-restored value to the one in memory.  (Duplicates 
>>aren't a problem as they'll just be dropped.) 
>>    
>>
>
>Since you are - pause - not worried about duplicates, you are 
>probably talking about pattern singletons?  Duplicates, even private
>Ones, are sort of bad style in Ruby, since you can easily access the 
>duplicates with ObjectSpace#each_object - therefore it might 
>have better to right out outlaw any kind of duplicates, but this
>not in keeping with the standard pattern singleton definition
>(developed for less dynamic languages). 
>
>  
>
>>If this can't be done, there are other approaches, but as 
>>they involve things like private class variables & classes 
>>that are only used internally as a cache.... well, the other 
>>approach looks cleaner, if it's possible.
>>    
>>
>
>Here is the marshaling example from (1.8) singleton.rb adopted
>to your situation - does this do what you want?
>
># example
>require 'singleton'
>
>class A
>  include Singleton
>  
>  def initialize
>    @hsh = {}
>    @ary = []
>  end
>  
>  def []=(key,val)
>    @hsh[key]=val
>  end
>  
>  def <<(o)
>    @ary << o
>  end
>  
>  private
>  
>  def _dump(depth = -1)
>    Marshal.dump([@hsh,@ary,tainted?],depth)
>  end
>  
>  def self._load(str)
>    instance.instance_eval {
>      h,a,t = *Marshal.load(str)
>      @hsh.merge h
>      @ary.concat a
>      if t 
>        taint
>      else
>        untaint
>      end
>    }
>    instance
>  end
>  
>  private_class_method :_load
>end
>
>
>/Christoph
>
>
>
>  
>