Question

Where is instance variable initialized as nil first time?
Can I redefine it as other value by default for all instances?

For example:

class Class
  #some code here or maybe in an Object class
end

class Foo1
  attr_accessor :bar
end

class Foo2
  attr_accessor :bar
end

p Foo1.new.bar # result is not nil
p Foo2.new.bar # result is not nil

This can be done by modifying the reader:

class Class
  def attr_accessor(attr_name)
    ...
    define_method "#{attr_name}" do
      if instance_variable_get "@#{attr_name}_history"
        instance_variable_get "@#{attr_name}_history"
      else
        "Not nil"
      end
    end
    ...
  end
end

But this doesn’t help in understanding the core of Ruby.
Many thanks!

Answer 1

Define a new method in class Class. Get instance variables through :instance_variables and set them to anything you like by using :instance_variable_set(:@var,default_value)

class Class

    alias oldNew new
        def new(*args)
        result = oldNew(*args)
        default = 2354 # set default here
        a = result.instance_variables
        a.each do
        |d|
        result.instance_variable_set(d,default)
        end

    return result
    end

end