From: Brian Candler <b.candler@...>
Date: 2010-02-16T18:11:38+09:00
Subject: Re: 'def', but with a closure

Brian Candler wrote:
> "The current class" is set inside a class ... end construct. But as 
> you've found, this starts a new scope. So you can use class_eval 
> instead, which sets both the current object and the current class.

Note that instance_eval sets the current class to the object's singleton 
class, whereas class_eval sets the current class to the object itself, 
if that object is a Class.

So this works:

@cars.each do |owner, model|
  widget = TkLabel.new(:text => model)
  widget.instance_eval do
    def get_owner
      "nobody"
    end
  end
end

Unfortunately, define_method is a method of Module, not Object. So this 
doesn't work:

@cars.each do |owner, model|
  widget = TkLabel.new(:text => model)
  widget.instance_eval do
    define_method(:get_owner) do
      owner
    end
  end
end

Hence the need for (class << widget; self; end).class_eval

Regards,

Brian.
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