From: Gregory Brown <gregory.t.brown@...>
Date: 2009-01-25T19:30:40+09:00
Subject: Question about BlankSlate.reveal

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.

-greg

[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