Learning Ruby - First Object

Learning how to construct an object in Ruby, this is what I have so far.

class Coin
  attr_reader :face, :value
  @@FaceRange = [0, 1]
  @@ValidValues = [1, 2, 5, 10, 20, 50, 100, 200]
  @@prng = Random.new # Pseudo-random Number Generator
  # Default Face to an illegal value so that it will flip the coin
  def initialize (value=10, face=-1) # CONSTRUCTOR
    self.value = value
    self.face = face
  end
  def face= (new_face)        # Set a valid face
    @face ||= 0 # default
    if @@FaceRange.include? new_face
      @face = new_face
    else
      self.flip
    end
  end
  def value= (new_value)      # Set a valid value
    @value ||= 1 # default
    @value = new_value if @@ValidValues.include? new_value
  end
  def set_face (new_face)     # Set face to a chosen value
     @face = new_face if [0, 1].include? new_face
  end
  def turn                    # Turn the coin over
     @face = (@face + 1).modulo(2)
  end
  def flip                    # Flip the coin
    @face = @@prng.rand(0..1)
  end
  def to_s # Over-ride the to_s method inherited from the Object class
    "Value is #{@value} Face is #{@face}"
  end
end

coin1 = Coin.new(20, 1)
puts coin1.face, coin1.value
puts coin1
coin1.set_face(0)
puts coin1

coin2 = Coin.new(50, 0)
puts "Coin 2 is #{coin2}"
coin2.set_face(0)
puts "Coin 2 is #{coin2}"
puts "Turn it"
coin2.turn
puts "Coin 2 is #{coin2}"
puts "Turn it"
coin2.turn
puts "Coin 2 is #{coin2}"

puts "Flip it"
coin2.flip
puts "Coin 2 is #{coin2}"
puts "Flip it"
coin2.flip
puts "Coin 2 is #{coin2}"
puts "Flip it"
coin2.flip
puts "Coin 2 is #{coin2}"
puts "Turn it"
coin2.turn
puts "Coin 2 is #{coin2}"

coin3 = Coin.new(5)
puts "Coin 3 is #{coin3}"

coin4 = Coin.new
puts "Coin 4 is #{coin4}"
puts "Flip it"
coin4.flip
puts "Coin 4 is #{coin4}"


$ ruby  coins2.rb
1
20
Value is 20 Face is 1
Value is 20 Face is 0
Coin 2 is Value is 50 Face is 0
Coin 2 is Value is 50 Face is 0
Turn it
Coin 2 is Value is 50 Face is 1
Turn it
Coin 2 is Value is 50 Face is 0
Flip it
Coin 2 is Value is 50 Face is 1
Flip it
Coin 2 is Value is 50 Face is 1
Flip it
Coin 2 is Value is 50 Face is 1
Turn it
Coin 2 is Value is 50 Face is 0
Coin 3 is Value is 5 Face is 1
Coin 4 is Value is 10 Face is 1
Flip it
Coin 4 is Value is 10 Face is 0

tjinkers@TJINKERS-LAP ~/ruby
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