From: Robert Klemme <shortcutter@...>
Date: 2009-04-03T15:49:31+09:00
Subject: Re: Class in a Class problem

On 03.04.2009 06:02, matt neuburg wrote:
> <denize.paul@gmail.com> wrote:
> 
>> My intent is to create a class that has access to call a method in an
>> instantiation of another class
>>
>> However my knowledge of Ruby classes (Ok classes in general) is
>> somewhat lacking
>>
>> The example below is a LOT simplified  But I need class B to call a
>> method within an instantiation of class A's.
>>
>> one alternative is to seperate the classes and then just do "b=B.new
>> (a)"  but I think that looks really messy and
>> - I have then to check a bunch of stuff about the parameter a
>> - I would have a world of more hurt trying to ensure that only one B
>> instantiation pointed to each a
>>
>> Can anyone help?  Or tell me that I am doing this all wrong.
>>
>>
>> Paul
>>
>> -----
>>
>> class A
>>   class B
>>     def initialize()
>>       puts "b init"
>>       print_stuff()
>>     end
>>   end
>>
>>   def B
>>     return B
>>   end
>>
>>   def print_stuff()
>>     puts "here"
>>   end
>> end
>>
>> a = A.new()
>> b = a.B.new()
> 
> Maybe I'm reading your question wrong, but the concept "has access to
> call" is misleading, it seems to me, since there is never lack of access
> in Ruby. So what you're really asking, I'm guessing, is that when a B
> instance is produced by an A instance, it should point to that A
> instance. We can do that without even giving the B class a name:
> 
> class A
>   def b
>     Class.new do
>       def initialize(a)
>         @a = a
>       end
>       attr :a
>     end.new(self)
>   end
>   # other stuff that an A knows how to do
> end

You are creating new classes all the time.  I don't think this is a good 
idea.

I am not sure what the OP really wants, if I'm not mistaken he wants to 
prevent creation of B instances outside of A and also make sure there is 
a 1:1 relationship between an A and a B instance.

First of all, the question is: why are they separated?  We can't answer 
that one from those abstract classes presented.

Hiding of class B for the outside could be done like this:

class A
   @b = Class.new do
     def print_stuff
       puts "hoho"
     end
   end

   def initialize
     @b = self.class.instance_variable_get("@b").new
     @b.print_stuff
   end
end

a = A.new
p a

But a) this is not really hidden and b) this looks quite ugly.

Paul, what are you trying to accomplish?

Kind regards

	robert