From: Michael Malone <michael.malone@...>
Date: 2009-04-03T11:17:28+09:00
Subject: Re: Class in a Class problem

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
>   

Here be dragons.  Have you considered the inheritance idea?  If a class 
*needs* access to another class's private variables, then the 
functionality either belongs in the same class or a child class.  Whilst 
this is technically legal, it really doesn't bode well. If you 
absolutely need Class A to have exactly one instantiation of Class B you 
might want to consider the Singleton design pattern for class B.  Which 
in ruby is _really_ difficult to implement...

include singleton #(or something along those lines) :)

and for B to be a class variable of A (@@b = B.new) which, if they act 
like Java statics (and I think they do) the class variable has one 
instantiation able to be accessed from any object of the class.

e.g
class B
  def initialize()
  end

  def to_s
    "This is class #{class}"
  end
end

class A

  @@b = B.new()

  def intitialize()
    puts @@b
  end

end

But in truth, you will have to be a little less generic to get a better 
answer.  If you can give more details of what you're trying to achieve, 
then please do, and I'll try and give better help.

Michael
> 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()
>
>   


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