Rails - Jun 2006 - Achieve pure object oriented design in Ruby (also posted on Ruby List)

Hi,

I have 3 classes A, B and C; I want to achieve following behavior (I am
calling it "pure object oriented designing") with them.

1.        An instance of Class C should not exist without instance of Class
B and instance of Class B should not exist without instance of Class A.

2.        Class A should be the only class accessible externally, i.e. one
should not be able to create/modify/delete instances of class B and class C
outside the scope of class A.

3.        For modifying member variables of class B and class C, an external
client should use class A.

4.        class A has multiple instances of class B associated with it and
similarly class B has multiple instances of class C associated with it.

Following are the classes with required methods and variables;


class A

#array of objects of class B associated with this instance

            @b_objs

#method to create instance of B and add it to above array

#methods to modify member variables of an instance of B and C (class C is
defined below)

end



class B

@b1

@b2

#array of objects of class C

            @c_objs

#method to create instance of C and add it to above array

 #methods to modify member variables of an instance of C

 end



class C

@c1

            @c2

 end

How would I achieve 4 points listed above?

 One solution I thought was to have nested classes as below,

 Class A

   Class B

            Class C

            end

   end

end

above approach satisfies all the points, but for point 3 above(For modifying
member variables of class B and class C, an external client should use class
A), there would be an overhead of adding a large number of wrapper methods
for members of classes B and C.

Is there any cleaner solution in ruby by which I can achieve above
requirements?
Thanks in Advance,
NAYAK
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