Liskov Substitution Principle

liskov.rb

class Rectangle
  attr_accessor :height, :width
  
  def calculate_area
    width * height
  end
end

class Square < Rectangle
  def width=(width)
    super(width)
    @height = width
  end
  
  def height=(height)
    super(height)
    @width = height
  end
end

rectangle = Rectangle.new
rectangle.height = 2
rectangle.width = 1
p rectangle.calculate_area

square = Square.new
square.height = 4
square.width = 2
p square.calculate_area

# We performed the same steps on parent and derived class 
#but we observed different behaviour. Interfaces of parent and derived class are not consistent.

#solved by creating two separate classes with their own behaviour.

class Shape
  def calculate_area
    raise NotImplementedError
  end
end

class Rectangle < Shape
  attr_accessor :height, :width
  
  def calculate_area
    height * width
  end
end

class Square < Shape
  attr_accessor :side_length
  
  def calculate_area
    side_length * side_length
  end
end

rectangle = Rectangle.new
rectangle.height = 2
rectangle.width = 1
p rectangle.calculate_area

square = Square.new
square.side_length = 4
p square.calculate_area