Lazy decorator pattern for ruby

gistfile1.rb

# Creates the ability to lazily initialize
# a class. This means the instance will not 
# be created until a method is called on it.
# Useful for objects that create connections or
# use other expensive resources.
# 
# example:
# 
# class ExpensiveObject
#   def initialize
#     @conn = Connection.new # this is really expensive
#   end
#   
#   def make_a_call
#     @conn.foo!
#   end
# end
# 
# usage:
# foo = LazyDecorator.new { ExpensiveObject.new } # note, at this point the connction has not yet been created
# foo.make_a_call # now the connection gets created
#
class LazyDecorator
  def initialize(&block)
    @init_block = block
  end
         
  def method_missing(sym, *args, &block)
    @instance ||= @init_block.call
    @instance.send sym, *args, &block
  end
end