ruby metaprogramming 03

最新推荐文章于 2017-12-14 17:29:46 发布

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本文介绍了Ruby中的元编程技术，包括eval及其变种如instance_eval、module_eval和class_eval的使用方法，以及如何通过class_variables_get、class_variables_set、instance_variable_get、instance_variable_set、const_get和const_set来操作类变量、实例变量和常量。

Refer to Metaprogramming in Ruby

eval

String can execute as code by eval which is a method of module Kernel.

instance_eval module_eval and class_eval

They are special type of evals.

Objects can use instance_eval to create methods. For classes, methods are class methods. Remember that anonymous class will be created.

module_eval and class_eval operates on classes and modules. By another word, they can not call on pure objects.

class_variables_get and class_variables_get

We can get and set class variables out of class.

class_variables

Method class_variables gives us a list of class variables.

instance_variable_get and instance_variable_set

They give us the ability to get and set the instance variable of object out of class.

const_get and const_set

They give us the ability to get and set the const out of class. Using them, we can even create classes in run time.

Object.const_set("Ruby", Class.new)
class_name = Object.const_get("Ruby")
class_name.class_eval do
  def hello
     puts "hello world"
  end
end

r = class_name.new
r.hello