From: Brian Candler <lists@...>
Date: 2012-05-23T04:28:13+09:00
Subject: Re: Changing self class from inside a method??

> you could probably either start with an empty array instead of nil, or
> "guard" all array methods with "ary ||= []".

A related and useful idiom is auto-vivification of Hash elements:

h = Hash.new { |h,k| h[k] = [] }
h[:foo] << "bar"
h[:foo] << "baz"
p h    # {:foo=>["bar", "baz"]}

Objects in ruby cannot change their class. If you really need to do 
this, then you can have a proxy object which delegates calls, and you 
can change the target object dynamically:

>> require 'delegate'
=> true
>> myvar = SimpleDelegator.new(nil)
=> nil
>> myvar.to_s
=> ""
>> myvar.__setobj__([])
=> []
>> myvar << "foo" << "bar"
=> ["foo", "bar"]

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