01.md

$ ruby thing.rb
[Calculator::LoggerDecorator, Calculator, Object, Kernel, BasicObject]
Calculator#div(10, 2) => 5

mimito.rb

module MagicLog
  def self.extended(receiver)
    decorator = Module.new
    receiver.prepend decorator
    receiver.const_set(:LoggerDecorator, decorator)
  end

  def log(name)
    self::LoggerDecorator.define_method(name) do |*args|
      result = super(*args)
      puts "#{self.class.name}##{name}(#{args.map(&:inspect).join(", ")}) => #{result}"
      result
    end
  end
end

class Calculator
  extend MagicLog

  log :div
  def div(x, y)
    x / y
  end
end

p Calculator.ancestors
Calculator.new.div(10, 2)