From: Robert Klemme <shortcutter@...>
Date: 2009-01-26T22:55:30+09:00
Subject: Re: Question about BlankSlate.reveal

2009/1/25 Gregory Brown <gregory.t.brown@gmail.com>:
> Hi folks,
>
> I've been working on a chapter for "Ruby Best Practices"[0] about the
> dynamic nature of Ruby, and I initially thought Jim Weirich's
> BlankSlate would be an excellent example (even though 1.9 has
> BasicObject).
> However, when I look at the reveal class method, I found what seems to
> be a fairly major limitation that I am having a hard time glossing
> over in my prose.
>
> The issue is that when you reveal a previously hidden method, the
> UnboundMethod that was stored gets bound to whatever the first
> instance is that calls the revealed method, because Jim's code caches
> the bound_method via a closure.  The best 'fix' I got was to drop the
> caching and rebind the method to self on every single method call, but
> I wasn't able to get away with that without saying "This is probably a
> performance nightmare".  Does anyone have a better suggested fix?  The
> original code for reveal, pulled from the builder gem, is below.

From what you write caching a bound method seems a bad idea because it
is instance specific. Caching of an unbound method would seem much
more reasonable (unless, that is, I am missing something).

On the other hand:

> [0] http://rubybestpractices.com
>
> ### Code pulled from blankslate.rb in the builder gem.
>
>    # Redefine a previously hidden method so that it may be called on a blank
>    # slate object.
>    def reveal(name)
>      bound_method = nil
>      unbound_method = find_hidden_method(name)
>      fail "Don't know how to reveal method '#{name}'" unless unbound_method
>      define_method(name) do |*args|
>        bound_method ||= unbound_method.bind(self)
>        bound_method.call(*args)
>      end
>    end
>  end

I do not really see caching that extends the instance on which #reveal
was invoked.  There is actually one closure per instance (more
correctly: one closure per call of reveal) and so no global cache.

Where exactly is your problem?

Cheers

robert


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