Achieve pure object oriented design in Ruby (also posted on

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.

  1.    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.

  1.    For modifying member variables of class B and class C, an 
    

external
client should use class A.

  1.    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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