From: E S <eero.saynatkari@...>
Date: 2005-02-09T15:51:10+09:00
Subject: Re: Creating objects from a template


> 
> L�hett�j�: "David McCabe" <davemccabe@gmail.com>
> Aihe: Creating objects from a template
> 
> Hi folks.
> 
> I'm pretty comfortable with Python, and I just decided to give Ruby a
> shot. I'm trying to duplicate a nifty method I use in Python to
> instantiate objects with properties that are loaded from a file.
> 
> My program is a war strategy game, which involves several different
> types of artillery units. Each type has properties such as range,
> speed, power, etc. I need to load these values from a file.
> 
> In python, my parser returns a hash of unit_type objects, where the
> names of units are the keys. Each time a unit is instantiated, it
> receives a unit_type object as an argument. Now here's the interesting
> part: it copies the instance variables from the unit_type into itself.
> 
> class Unit(object):
>       def __init__(self, type):
> 	  self.type = type
> 	  self.__dict__.update(self.type.__dict__)
> 
> There's more to it than that, but that's the interesting part. So now
> I can say:
> 
>       my_new_unit = Unit(types["Panzer"])
> 
> And I'll get a Unit object with all the values for Panzers
> initialized.
> 
> drbrain on #ruby-lang came up with this:
> 
> http://rafb.net/paste/results/lgb4xv42.html
> 
> It looks like it'll do what I want. There's only one deficiency: I
> would have to list out every possible proporty of a unit in two
> seperate places in the source. In the python version, I don't have to
> list it at all. Whatever properties are in the config file are loaded
> into the object.
> 
> So, now I'm looking for any pointers on ways to do this.

Well, a *really* simple solution would be this:

class Object
  def steal_ivs(other)
    other.instance_variables.each do |iv|
      self.instance_variable_set(iv, other.instance_variable_get(iv))
    end
  end
end

I'll leave the elegant stuff to the gurus.

> Thanks!

E