classvars.rb

class Polygon
  @@sides = nil
  def self.sides
    @@sides
  end

  def self.count
    @@count
  end

  @@count = 0

  def initialize
    @@count += 1
  end
end

class Triangle < Polygon
  @@sides = 3
end

class Square < Polygon
  @@sides = 4
end

pry-session.rb

[1] pry(main)> require './classvars'
=> true

# This makes sense
[2] pry(main)> Polygon.count
=> 0
[3] pry(main)> p = Polygon.new
=> #<Polygon:0x007fb0a1ec3cc8>
[4] pry(main)> t = Triangle.new
=> #<Triangle:0x007fb0a1ab01b8>
[5] pry(main)> s = Square.new
=> #<Square:0x007fb0a3080290>
[6] pry(main)> Polygon.count
=> 3

# This doesn't!
[10] pry(main)> Square.sides
=> 4
[11] pry(main)> Triangle.sides
=> 4

I totally trolled this out of the stream.

Looks like this is a scope resolution problem with static properties. In php you can use self:: to access the local member, parent:: to access the parent, and in the parent, when wanting to use the child's property you can use static:: which uses runtime scope resolution unlike self:: and parent:: which are bound at compile time.

Does ruby not have a way to represent that hierarchy?

Yeah, ruby class variables are shared by all subclasses. I wrote this for demonstration purposes.