[Rubycocoa-talk] Programmatically overriding 0-arity ObjC methods

[sergio <sde...@gm...>]

Hi all,

this is my first post to this list.

I have been recently playing with metaprogramming a RubyCocoa app  
using Core Data, and I got into a behaviour I don't fully understand  
when programmatically overriding an NSManagedObject method that takes  
no parameters, as didSave or awakeFromInsert.

Say I have the following bit of code :

class RCEntity < OSX::NSManagedObject

     ....

     def self.makeEntity(...)

        define_method(:awakeFromInsert) do
            super_awakeFromInsert
            # more stuff here
        end

     end
end

class TestEntity < RCEntity
     makeEntity(...)
end

(this code is not meant to be run)

What I expect is that, due to the call to makeEntity, awakeFromInsert  
is  overriden by TestEntity. What I get is the following error message:

/Library/Frameworks/RubyCocoa.framework/Versions/A/Resources/ruby/osx/ 
objc/oc_import.rb:318:in `_ns_behavior_method_added': Cannot override  
Objective-C method 'awakeFromInsert' with Ruby method  
#awakeFromInsert, they should both have the same number of arguments.  
(expected arity 0, got -1) (RuntimeError)

I am getting this behaviour in RubyCocoa 0.12.0 and 0.11.1. The same  
code works under RubyCocoa 0.10.1 (and previous versions that used  
the ns_override directive). Furthermore, this behaviour only is shown  
when overriding methods that take no parameters; everything works  
fine when overriding, say, willChangeValueForKey, which takes one  
parameter. I tried to override the didSave method as well (no  
parameters), and it also failed, so it seems to be related to the  
number of parameters.

Of course, overriding always works when I am not doing it via  
define_method but plainly in the class definition.

Any clues anyone? I am willing to explore further this issue on my  
own, provided there is no easy explanation, if someone is so kind to  
point me in the right direction....

Thanks in advance and best
sergio