class Foo
  def self.inherited(subclass)
    puts "#{subclass.inspect} inherited from #{self}"
  end
end

class Bar < Foo
end

a = Class.new(Bar) do
  def self.to_s
    "some other class"
  end
end

Bar inherited from Foo
#<Class:0x0000010086c198> inherited from Bar

Bar inherited from Foo
some other class inherited from Bar