From: squidster@... (Squidster)
Date: 2002-11-15T15:22:34+09:00
Subject: (Simple/Naive) Deep Copy Implementation

Rubyists,
I wanted to have a deep-copy mechanism in order to protect my precious
data from getting all trampled over by a client class, and was both
surprised and frustated by the lack of a native deep-copy in Ruby.

Since then, I've scanned the archive and came across the
Marshal.load/dump "hack" to do deep-copy. Well, tried that and Marshal
just doesn't cut the mustard for me, and my data doesn't even have
"weird" objects like IO or contextual binding, just hashes and arrays,
albeit they are very deeply nested.

Well, I got off my figurative butt and decided (like a good OSS/FSF
devotee) to take things into my own hands. I have now a working
mechanism for my needs.

Some disclaimers:
1. Although this works for me, YMMV
2. DOESN'T support singletons, bindings, etc.
3. DOESN't support IO
4. DOES support recursion
5. DOES support complex nesting (I hope :-p)
6. DOES support user classes, arrays, and hashes

Well, 'nuff said. Here's the code and feel free to improve upon it.

-------------------------- C U T --------------------------
#!/usr/bin/ruby -w

module DeepClone
	alias shallow_clone clone
	def clone
		klone = self.shallow_clone
		self.instance_variables.each { |v|
			vari = v[1..-1]
			val = send(vari).clone
			klone.send("#{vari}=", val)
		}
		return klone
	end
end
class Hash
	alias shallow_clone clone
	def clone
		klone = self.shallow_clone
		self.each { |k,v| klone[k] = v.clone }
		return klone
	end
end
class Array
	def clone
		# FIXME: Not cloning, am rebuilding from scratch!!
		klone = Array.new 
		self.each { |v|
			klone << v.clone
		}
		return klone
	end
end
class Fixnum
	def clone
		return self
	end
end
class Bignum
	def clone
		return self
	end
end
class NilClass
	def clone
		return self
	end
end
class FalseClass
	def clone
		return self
	end
end
class TrueClass
	def clone
		return self
	end
end
 

class SD
	attr_accessor :sub, :tot, :stud

	def initialize sub, tot
		@sub	= sub
		@tot 	= tot
		@stud	= Hash.new
	end
end   

class User
	attr_accessor :subj_dist
	def initialize subj_dist
		@subj_dist = subj_dist
	end
end


foo = {"ssk1234" => SD.new("ssk1234", 44)}
ctx = User.new foo

ctx.subj_dist["ssk1234"].stud =
	{"foo"=>[1,3,45,nil],"bar"=>[4,23,false,2242],"baz"=>[true,3425,23]}


include DeepClone
clone_ctx = ctx.subj_dist.clone
clone_ctx["ssk1234"].stud.delete "foo"

puts "ctx:       #{ctx.subj_dist.inspect}"
puts "clone_ctx: #{clone_ctx.inspect}"
-------------------------- C U T --------------------------