From: Joel VanderWerf <vjoel@...>
Date: 2006-12-12T05:11:40+09:00
Subject: Re: Question on IO objects, initialize, and yaml

Mark Noworolski wrote:
> Say I have a class with pseudo code as follows:
> class Test
> def initialize
>  @a=1
>  @b=File.open("file+Time.now or similar")
> end
> end
> 
> Now, imagine that I use this class for a while and then I want to dump 
> it to
> a YAML file.
> 
> When I restart my code, I want it to read in stuff from the YAML file 
> (if it
> exists) and use that as a starting point to work from (basically, I am
> saving state in the yaml file). You'll note that I cannot just do this as
> is, because reading in from YAML does not initialize the class, so @b would
> not be initialized correctly on restart.
> 
> I'd like to just initialize the thing, then read in the YAML file to
> overwrite the state with the saved values. Is there some extremely obvious
> ruby way to do this or something equivalent?

A possible alternative is to be lazy about constructing the non-dumpable 
stuff:

[~] cat test.rb
require 'yaml'

class Test
   def initialize
     @a = 1
   end
   def b
     @b ||= File.open(__FILE__) # just for testing
   end
end

t = Test.new
t2 = YAML.load(YAML.dump(t))

line = t2.b.gets
p line

[~] ruby test.rb
"require 'yaml'\n


If you do this, other parts of your code shouldn't access @b directly. 
Instead, call the #b method.

-- 
       vjoel : Joel VanderWerf : path berkeley edu : 510 665 3407