# Given the following code

class BaseClass
end

class ClassA < BaseClass

  @@instances = []
  attr_accessor :name

  def initialize(name)
    @name = name
    @@instances << self
  end

  def self.list
    @@instances
  end

  def to_s
    @name
  end

end

class ClassB < BaseClass

  @@instances = []
  attr_accessor :name

  def initialize(name)
    @name = name
    @@instances << self
  end

  def self.list
    @@instances
  end

  def to_s
    @name
  end
end

puts "Creating instanes"
a = ClassA.new "a"
aa = ClassA.new "aa"
b = ClassB.new "b"

puts "Listing for ClassA"
puts ClassA.list
puts "Listing for ClassB"
puts ClassB.list

# We get the following output

bash-3.2$ ./test1.rb
Creating instanes
Listing for ClassA
a
aa
Listing for ClassB
b

Perfect, however we could do with deduping

class BaseClass
  @@instances = []
  attr_accessor :name

  def initialize(name)
    @name = name
    @@instances << self
  end

  def self.list
    @@instances
  end

  def to_s
    @name
  end
end

class ClassA < BaseClass
end

class ClassB < BaseClass
end

puts "Creating instanes"
a = ClassA.new "a"
aa = ClassA.new "aa"
b = ClassB.new "b"

puts "Listing for ClassA"
puts ClassA.list
puts "Listing for ClassB"
puts ClassB.list

However, when we run this we get

bash-3.2$ ./test2.rb
Creating instanes
Listing for ClassA
a
aa
b
Listing for ClassB
a
aa
b

This makes sense because @@instances was defined in the BaseClass and so would be shared between ClassA and ClassB.

The question is, what is the best way to deduplicate the first example to look more like the second example, but with the correct output?