From: "David A. Black" <dblack@...>
Date: 2008-10-20T20:19:10+09:00
Subject: Re: define_method inside a module

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

etc.


David

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