From: Robert Klemme <shortcutter@...>
Date: 2008-10-20T20:42:12+09:00
Subject: Re: define_method inside a module

2008/10/20 David A. Black <dblack@rubypal.com>:
> Hi --
>
> On Mon, 20 Oct 2008, MR Damien wrote:
>
>> Joel VanderWerf wrote:
>>>
>>> MR Damien wrote:
>>>>
>>>>  def add(object)
>>>>      end
>>>>    end
>>>>  end
>>>> end
>>>> undefined method `define_method' for #<Test:0x2ce631c> (NoMethodError)
>>>
>>> Try working in the singleton class:
>>>
>>> class C
>>>   def foo
>>>     class << self
>>>       define_method :bar do puts "BAR"; end
>>>     end
>>>   end
>>> end
>>>
>>> c = C.new
>>> c.foo
>>> c.bar
>>
>> Hi,
>>
>> seems not to work neither
>>
>>
>> ------------------
>> def add(object)
>>   name = "@" + self.collection_name_for(object)
>>
>>   if self.instance_variable_get(name)
>>     self.instance_variable_get(name) << object
>>   else
>>     self.instance_variable_set(name, Array.new)
>>     self.instance_variable_get(name) << object
>>
>>     class << self
>>       define_method(name) do
>>         instance_variable_get("@#{name}")
>>       end
>>     end
>>
>>   end
>>  end
>> ------------------
>> in `define_method': interning empty string (ArgumentError)
>
> That's because name is not in scope inside the class definition body
> (class << self). In order to keep name in scope, you need to use
> class_eval on the singleton class. That way, you're operating inside a
> code block, which does share the local variables.
>
>  (class << self; self; end).class_eval do
>    define_method(name) do

Also, watch closely the contents of "name" and how you (OP) use it.

robert


-- 
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