Question

I have something like the following

class A 

  def initialize
    @var = 0
  end

  def dosomething
      @var+=1
  end

end

class B < A

 def initialize
   super
 end
 def func
    puts @var
 end
end

The problem is when I call

 a = A.new
 a.dosomething
 b = B.new

the value which @var returns is 0 how would I change my code so it would return the “new” value of var (1)?

Answer 1

Quick answer, for if you actually understand Classes, Inheritance and Objects : replace @var (an instance variable, and therefore different in a and b) with @@var (a class variable, and therefore the same in all instances of class A).

Otherwise, your question indicates you have a fundamental misunderstanding of what’s going on with classes, objects and inheritance.

Your code does the following:

• Defines a class, called A. This is essentially a blueprint from which you can create objects.
  • Declares that when an object of type A is created, that object should be given it’s own private copy of an attribute, called var, which is set to 0.
  • Declares that objects of type A can be asked to dosomething, which increases the value of that object’s var by 1.
• Defines a class called B, which is a special case of an A

Therefore, in your second snippet, you create an object a, which is an A. It has its own attribute called var, which is set to 0 and then incremented. You then create b, which is a B (and is therefore also an A). b has its own attribute called var, separate from a‘s var, which is set to 0.