From: Sergey Volkov <gm.vlkv@...>
Date: 2006-05-11T17:33:22+09:00
Subject: Re: plz help with binding

Sorry, guys,
I must admit - I was not right about Ruby closures;
most probably about metaprogramming neither,
so, please disregard my previous message;

closures work in Ruby perfectly, my mistake was that arr_meth was executed 
only once inside class definition:
#
class C
    def self.arr_meth( sym )
        arr = []
        define_method sym.to_sym, lambda{ arr }
    end
    arr_meth :arm
end
#
closure was created, but it was then shared between all class instances, so 
Ara was absolutely right - we have to create new closure for each individual 
instance, and this can not be implemented on class level (no instances 
yet!);

I still do not want to modify class code to add instance_var-less storage, 
so at this moment I have implemented external function to extend class with 
new method (thanks, Ara!):
#!/bin/ruby
module M
    def self.add_loc obj, name, ini=[]
        skl = class << obj ; self ; end
        skl.module_eval{
           v = ini
           define_method name.to_sym, lambda{ v }
        }
    end
end
#
ca = Object.new
M.add_loc ca,:pocket; ca.pocket << 10
M.add_loc ca,:bag; ca.bag << :book
#
cb = Object.new
M.add_loc cb,:pocket; cb.pocket << 20
M.add_loc cb,:bag; cb.bag << :apple
#
p [ca.pocket, ca.bag]
p [cb.pocket, cb.bag]
---------- Capture Output ----------
[[10], [:book]]
[[20], [:apple]]

Hidden instance slots created! In this example they contain array, but 
accessors can be implemented without any problem.
Any ideas about better API?
thanks
regards
Sergey
--
oh - please do not forget to be kind!

----- Original Message ----- 
From: "Sergey Volkov" <gm.vlkv@gmail.com>
To: "ruby-talk ML" <ruby-talk@ruby-lang.org>
Sent: Thursday, May 11, 2006 3:39 AM
Subject: Re: plz help with binding


> This is cool!
> But not for average (read big enterprise) level programmer :(
> How can I follow 'keep it simple, stupid!' approach with Ruby 
> metaprogramming?
> How many Ruby programmers can reproduce this code with easy?
> Can such code code be supported in production environment?
>
> I'm not asking, I'm crying!
> I'd like to ask Matz: give me real lexical closure and clean up meta class 
> mess, please!!!
>
> Or should we admit, that Ruby metaprogramming is for real programmers 
> only?
> Or I'm just plain stupid?
>
> Please advise;
> thanks
> bests
> Sergey
>
> ----- Original Message ----- 
> From: <ara.t.howard@noaa.gov>
> To: "ruby-talk ML" <ruby-talk@ruby-lang.org>
> Sent: Thursday, May 11, 2006 2:11 AM
> Subject: Re: plz help with binding
>
>
>> On Thu, 11 May 2006, Sergey Volkov wrote:
>>
>>> Now I'm trying to create instance-var-less storage:
>>
>> an even trickier way:
>>
>>   harp:~ > cat a.rb
>>   class C
>>     def self.arr_meth m
>>       m = m.to_s
>>       define_method(m) do
>>         singleton_class =
>>           class << self
>>             self
>>           end
>>         singleton_class.module_eval do
>>           a = []
>>           define_method m, lambda{ a }
>>         end
>>         send m # recurse into newly defined method
>>       end
>>     end
>>
>>     arr_meth :arm
>>   end
>>
>>   ca = C.new; ca.arm << 10
>>   cb = C.new; cb.arm << 20
>>
>>   p ca.arm #-> [10, 20]
>>   p cb.arm #-> [10, 20]
>>   p( ca.arm.eql?( cb.arm ) ) #-> true
>>
>>   harp:~ > ruby a.rb
>>   [10]
>>   [20]
>>   false
>>
>> -a
>> -- 
>> be kind whenever possible... it is always possible.
>> - h.h. the 14th dali lama