Ruby: Non-instantiable parent class with instantiable subclasses

alternate_parent.rb

class AlternateParent
  def self.new(*args)
    raise NoMethodError, "cannot instantiate #{self.name}" if self == AlternateParent
    super
  end
  
  def initialize(num)
    @num = num
  end
end

alternate_sub_class.rb

class AlternateSubClass < AlternateParent
  def initialize(num)
    super
    @sub_num = num * num
  end
end

irb.rb

Parent.new(5)
# NoMethodError: undefined method `new' for Parent:Class

SubClass.new(5)
#<SubClass:0x007fcfde857950 @num=5, @sub_num=25>

AlternateParent.new(5)
# NoMethodError: cannot instantiate AlternateParent

AlternateSubClass.new(5)
#<AlternateSubClass:0x007fcfde8565c8 @num=5, @sub_num=25>

parent.rb

class Parent
  class << self
    undef_method :new
    
    def inherited(sub_class)
      sub_class.define_singleton_method(:new) do |*args|
        Class.instance_method(:new).bind(sub_class).call(*args)
      end
    end
  end
  
  def initialize(num)
    @num = num
  end
end

sub_class.rb

class SubClass < Parent
  def initialize(num)
    super
    @sub_num = num * num
  end
end