From: Mathieu Bouchard <matju@...>
Date: 2001-10-24T20:49:17+09:00
Subject: [ruby-talk:23181] Re: obj.__dict__


On Wed, 24 Oct 2001, Rich Kilmer wrote:

> So...in Python you can use this:
> obj.__dict__['attrName']=value
> ...to get direct access to (get/set) the values of every attribute on
> an object.
> 
> In Ruby every object attribute is private and can only be accessed
> through a method...period.  Exposing the __dict__ "bag" on an object
> exposes the entire state of that object for public consumption.

Which reminds me that I wrote a Ruby emulation of obj.__dict__ 5 months
ago. I finally checked-in this nice sample of M�taRuby usage this morning.
(this is one-third of samples/ReflectionHashes.rb).

----------------8<----------------cut-here----------------8<----------------

class InstanceVariablesHash; include HollowHash, SimpleHashP

	# victim is any object.
	# it only works on Ruby-visible instance-variables,
	# i.e. those accessible by "@" names.
	def initialize(victim)
		@victim = victim
	end

	def length
		@victim.instance_variables.length
	end

	def canonize_name(k)
		if Symbol===k; k=k.to_s; end
		String===k && k =~ /^(@[A-Za-z_]\w*)$/ or
			raise "Invalid Name"
		k
	end

	def has_key?(k)
		k = canonize_name k
		!! @victim.instance_variables.index(k)
	end

	def get(k)
		k = canonize_name k
		@victim.instance_eval k
	end

	def put(k,v)
		k = canonize_name k
		@victim.instance_eval "#{k} = ObjectSpace._id2ref(#{v.id})"
	end

	def remove(k)
		# the best I can do
		put(k,nil)
	end

	def each_key(&proc)
		@victim.instance_variables.each(&proc)
	end
end

----------------8<--------------d�coupez-ici--------------8<----------------

> methods.  The same is NOT true for Python.  It provides "privacy"
> through obfuscation (name mangling) but its still easy to get around
> (because everything is still held in the __dict__).

Well, this may be interesting from a $SAFE perspective. If you are not
coming this way from a $SAFE perspective, chances are that I don't give
a...

________________________________________________________________
Mathieu Bouchard                   http://hostname.2y.net/~matju