Instance Variables Inheritance

Question

Can someone explain how a class can access the instance variables of its superclass and how that is not inheritance? I\'m talking about \'The Ruby Programming Language\' and the

Answer 1

You can compare these two examples.

example 1: it seems B inherit @i from A.

class A
  def initialize()
    @i = "ok"
  end
end

class B < A
  def print_i()
    p(@i)
  end
end

B.new().print_i()   # Shows "ok"

example 2: if B has its own initialize(), it cannot find @i.

class A
  def initialize()
    @i = "ok"
  end
end

class B < A
  def initialize()
  end

  def print_i()
    p(@i)
  end
end

B.new().print_i()   # nil, print nothing

class B's @i in example 1, is actually created implicitly by A#initialize() when you invoke B.new().

In your case, @x and @y in Point3D is actually created by Point#initialize(), not inherited from Point