From: Robert Klemme <shortcutter@...>
Date: 2010-02-15T17:28:37+09:00
Subject: Re: 'def', but with a closure

2010/2/15 Albert Schlef <albertschlef@gmail.com>:
> It occurred to me several times that I wanted to do:
>
>  @cars.each do |owner, model|
>    widget = TkLabel.new(:text => model)
>    def widget.get_owner
>      return owner
>    end
>  end
>
> But, of course, this doesn't work because the code inside 'def' doesn't
> see the enveloping variables, so the 'owner' within the 'def' isn't
> recognized.
>
> So instead I do:
>
>  @cars.each do |owner, model|
>    widget = TkLabel.new(:text => model)
>    meta = (class << widget; self; end)
>    meta.send(:define_method, :get_owner) do
>      return owner
>    end
>  end
>
> It work. Yet, it looks a bit ugly. Is there any "nicer" way I'm missing?

You can at least shorten it a bit

 @cars.each do |owner, model|
   widget = TkLabel.new(:text => model)
   (class << widget; self; end).send(:define_method, :get_owner) do
     owner
   end
 end

I find this better than other approaches because storing in an
instance variable is not the same as using the closure.  Josh's
approach with eval has the disadvantage of a) using eval in the first
place, b) it does not work for all types of objects handed in as owner
and c) for Strings it's less efficient because it will create a new
String instance every time the method is invoked.

Kind regards

robert

-- 
remember.guy do |as, often| as.you_can - without end
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