From: Intransition <transfire@...>
Date: 2010-08-24T10:35:59+09:00
Subject: Re: Your thoughts on #memo ?



On Aug 23, 1:52 pm, Benoit Daloze <erego...@gmail.com> wrote:
> On 23 August 2010 17:18, Intransition <transf...@gmail.com> wrote:
>
>
>
> > Like to get some thoughts on the following technique for memoization:
>
> >  # Memoize a method.
> >  #
> >  #   class MemoExample
> >  #     attr_accessor :a
> >  #     def m
> >  #       memo{ @a }
> >  #     end
> >  #   end
> >  #
> >  #   ex = MemoExample.new
> >  #
> >  #   ex.a = 10
> >  #   ex.m  #=> 10
> >  #
> >  #   ex.a = 20
> >  #   ex.m  #=> 10
> >  #
> >  def memo(&block)
> >    key = eval('__method__', block)
> >    val = block.call
> >    singleton_class = (class << self; self; end)
> >    singleton_class.__send__(:define_method, key){ val }
> >    val
> >  end
>
> > Downside / upsides to the approach? Any suggestions for improvement?
> > Or is this just an altogether bad idea?
>
> It looks a bit weird, and eval is really ugly^
>
> I recently wrote two crazy implementations of memoize:
>
> http://github.com/eregon/project_euler/blob/master/014.rb#L64-93
>
> The second seems rather inefficient, while the first seems good.
> I'm here saving the only argument to determine what to cache.
>
> It is pretty bad because it redefines the method, however all the
> meta-programming stuff is rather interesting, I think.
>
> What do you think of it?

I find the approach of extending Method interesting. I will have to
play with that.

Are you always getting the same method object and thus the same cache
for memoize2?