From: Joel VanderWerf <vjoel@...>
Date: 2004-03-25T06:33:19+09:00
Subject: Re: Dynamically define method

rolo wrote:
> 
> I need something like this
> 
> 	def on_success(&block)
> 		@event['success'] = block
> 	end
> 
> I want the above method to be defined dynamically 
> 
> 	def define_my_method(symbol)
> 	....
> 	...
> 	....
> 	....
> 	end
> 
> 	any call to define_my_method(:success) should result in 
> 
> 	def on_success(&block)
> 		@event['success'] = block
> 	end
> 
> 	and will be used as
> 
> 	myobject.on_success(){
> 		p "Success"
> 	}
> I tried using define_method but am having problems in passing a block.

I think that's just a limitation of define_method--you can define a 
method with a specified a parameter list, but not with the ability to 
receive a block. The first example below is the best I could come up 
with using define_method--you've probably gotten this far as well. The 
second example works as you want (AFAIU), but uses class_eval.

===============
class C
   def self.define_my_method(symbol)
     define_method("on_#{symbol}") do |handler|
       @event ||= {}
       @event[symbol] = handler # Proc.new fails
     end
   end

   define_my_method "success"
   define_my_method "failure"

   def handle(condition)
     @event[condition].call
   end
end

c = C.new

c.on_success(proc {
   puts "handled success"
})

c.on_failure(proc {
   puts "handled failure"
})

c.handle("success")
c.handle("failure")
===============

===============
class C
   def self.define_my_method(symbol)
     # should check that symbol is legit
     class_eval %{
       def on_#{symbol}(&handler)
         @event ||= {}
         @event["#{symbol}"] = handler
       end
     }
   end

   define_my_method "success"
   define_my_method "failure"

   def handle(condition)
     @event[condition].call
   end
end

c = C.new

c.on_success do
   puts "handled success"
end

c.on_failure do
   puts "handled failure"
end

c.handle("success")
c.handle("failure")
=================