From: Junyoung Kim <jykim@...>
Date: 2008-11-26T13:53:41+09:00
Subject: Re: How to use a passing argument(returned argument)?

Einar's suggestion is very good and clear everything for me :)

finally, my code should be changed like -->

   class Reference
       def initialize(var_name, vars)
           @getter = eval "lambda { #{var_name} }", vars
           @setter = eval "lambda { |v| #{var_name} = v }", vars
       end
       def value
           @getter.call
       end
       def value=(new_value)
           @setter.call(new_value)
       end
   end

   def ref(&block)
       Reference.new(block.call, block.binding)
   end

   def set10(var_a)
       var_a.value = 10
   end

   a = 22
   set10 (ref{:a})
   p a

thanks for all :)

2008. 11. 26, 오후 1:38, Einar Magnús Boson 작성:

>
> On 26.11.2008, at 04:19 , Joshua Ballanco wrote:
>
>> On Nov 25, 2008, at 8:49 PM, 김 준영 wrote:
>>
>>> Hello, everyone !!!
>>
>> Hi there!
>>
>>> I have question about how to use a passing argument. firstly let  
>>> me show sample code.
>>>
>>> a = 0
>>>
>>> def set10(aArg)
>>> 	aArg = 10
>>> end
>>>
>>> set10(a)
>>>
>>> p a <--- I wanna get 10 as a result.
>>>
>>>
>>> How can I do for this one?
>>
>> First, the pattern you are looking for is not very object oriented- 
>> y. That is, you're asking to remove some of the logic pertaining to  
>> 'a' and put it somewhere outside of 'a'. Since 'a' is an object  
>> (everything in Ruby is), then it would be best if you made 'a' an  
>> instance of a class with the 'set10' logic in it. The sort of pass- 
>> by-reference pattern you're looking for is much more typical of C.
>>
>> That said, this would be, I think, the closest equivalent in Ruby:
>>
>> a = 0
>>
>> def set10(aArg_name,  bind)
>> eval("#{aArg_name} = 10", bind)
>> end
>>
>> set10('a', binding)
>>
>> p a
>>
>> => 10
>>
>> Cheers,
>>
>> Josh
>>
>>
>
>
> I did not know this, google filled me in and this might be relevant  
> to the original question:
> http://onestepback.org/index.cgi/Tech/Ruby/RubyBindings.rdoc/style/print
>
> They end up with this:
>
>  def swap(aref, bref)
>  aref.value, bref.value = bref.value, aref.value
>  end
>
>  a = 22
>  b = 33
>  swap(ref{:a}, ref{:b})
>  p a                       # => 33
>  p b                       # => 22
>
> Pretty neat, if that's something you wanna do. Makes me wonder  
> though: when I first saw this (5 minutes ago) I thought you might be  
> able to do
>
> a = 0
>
> def set10(aArg_name,  bind=binding)
> eval("#{aArg_name} = 10", bind)
> end
>
> set10('a')
>
> p a
>
>
> but that doesn't work, in what context and when are default-values  
> evaluated? my guess is that they get the same closure as the method  
> body and are evaluated on call, is that correct?
>
> einarmagnus
>
>
>
>