From: Igor Pirnovar <lists@...>
Date: 2012-10-20T07:47:24+09:00
Subject: Re: About define_method

li shoubo wrote in post #1079862:
> I want to define a method in kernel using Flattern Scope.
>
>   Kernel.send :define_method, :each_event do
>     events.each_pair do |message, condition|
>       yield message, condition
>     end
>   end
 . . .
> However, if I use send define_method method to define each_event, I
> would met a exception:
> in `each_event': no block given (LocalJumpError)
>
> I do not know why? if I do not use "send", the "yield" work well. Also,
> I can define method as follows according to "meta programming ruby"
> says:
>
>   Kernel.send :define_method, :each_event do |&block|
>     events.each_pair do |message, condition|
>       block.call message, condition
>     end
>   end

The problem is not the 'send', but rather the 'define_method'. Namely,
'define_method' does not allow you to specify a method body that expects
a blok. If you need to dynamically create a method that accepts a block,
you need to use the 'def method_name; ...; end' and the 'class_eval'
(see: D. Flanagan's & Y. Matsumoto's book 'The Ruby Programming
Language' page:275).

So, your example should look something like the following:

  Kernel.class_eval do
    def each_event(events)
      events.each_pair do |message, condition|
        yield message, condition
      end
    end
  end
  events = { one: 1, two: 2, three: 3 }
  each_event(events) { |x, y| puts "#{x}, #{y}" }

Regards, igor

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