From: Phrogz <gavin@...>
Date: 2006-10-06T03:35:15+09:00
Subject: Re: Associating data with a function

Trans wrote:
> I look at this and think, "where the persistant locals?" Well, we don't
> have em but they can be emulatated via instance vars.
>
>  class Foo
>    def c1
>      tmp1 = (@_tmp1 ||= ExpensiveObject.new)
>      tmp2 = (@_tmp2 ||= ExpensiveObject.new)
>      # stuff involving tmp1/tmp2
>      result = tmp1 + tmp2 + c2
>    end
>    def c2
>      tmp1 = (@_tmp1 ||= ExpensiveObject.new)
>      tmp2 = (@_tmp2 ||= ExpensiveObject.new)
>      # stuff involving tmp1/tmp2
>      result = tmp1 + tmp2
>    end
>  end

Persistent locals is an interesting concept. Your specific example
fails, however, if I change c1's last line to:
    result = tmp1 * c2 + tmp2
because calculating c2 will change the value in @_tmp2, making the tmp2
in c1 invalid. You'd need to ensure that each instance variable had a
unique name in each function, which is just about the same as declaring
all the instance variables during initialization or class creation.