class Klass
     def hello(*args)
       "Hello " + args.join(' ')
     end
end
k = Klass.new
k.send :hello, "gentle", "readers"   #=> "Hello gentle readers"

send其實就是動態地根據名字呼叫函式，傳遞後面的內容作為呼叫引數，api函式原型為：
obj.send(symbol [, args...]) => obj

作為指令碼語言，ruby自然也有eval這樣的函式，除此之外，還有instance_eval和class_eval
instance_eval感覺就是取出物件的裡的變數
class Klass
 

     def initialize
       @secret = 99
     end
end

k = Klass.new
k.instance_eval { @secret }   #=> 99

class Thing
end
a = %q{def hello() "Hello there!" end}
Thing.module_eval(a)
puts Thing.new.hello()   =>  "Hello there!"

在rails裡的action_controller.rb裡
ActionController::Base.class_eval do
  include ActionController::Flash
  include ActionController::Filters
。。。。
end