#from your book
    
    def distance(*points)
      case(points.length)
      when 2
        x1,y1,x2,y2 = points.flatten
      when 4
        x1,y1,x2,y2 = points
      else
        raise ArgumentError, "Points may be specified as [x1,y1], [x2,y2] or x1,y1,x2,y2"
      end
      Math.hypot(x2 - x1, y2 - y1)
    end

    puts distance(1, 2, 5, 6)
    puts distance([1, 2], [5, 6])

    # why would you choose to make a complicated interface that requires a complicated implementation?

    # simple, clear interfaces that allow for simple implementations
    # are almost always preferrable to complicated ones that save a
    # keystrokes through syntax

    class Point
      attr_accessor :x
      attr_accessor :y
  
      def initialize
        self.x = 0
        self.y = 0
      end
  
      def self.with(x, y)
        new.set(x, y)
      end
  
      def set(x, y)
        self.x = x
        self.y = y
        self
      end
  
      def distance_to(a_point)
        Math.hypot(a_point.x - x, a_point.y - y)
      end
    end

    puts Point.with(1, 2).distance_to(Point.with(5, 6))