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Ruby 中的 module_function 和 extend self異同

更新時(shí)間：2017年05月23日 08:49:03 作者：hww_面條醬

本文主要給大家介紹了在Ruby中 module_function 和 extend self的共同點(diǎn)和區(qū)別，非常的詳細(xì)，也很實(shí)用，方便大家更好的理解的module_function 和 extend self

在閱讀開(kāi)源的 Ruby 代碼和編寫可維護(hù)性的代碼經(jīng)常遇到這兩者的使用，那么他們兩者的共同點(diǎn)和區(qū)別是什么呢？

module_function

Ruby 的 module 是 method 和 constants 的集合。module 中的method 又可分為 instance method 和 module method, 當(dāng)一個(gè) module 被 include 進(jìn)一個(gè) class ,那么 module 中的 method (注：沒(méi)有被 module_function 標(biāo)記的 method)就是 class 中的 instance method, instance method 需要所在的 class 被實(shí)例化之后才能被調(diào)用；被 module_function 標(biāo)記的 method（不管該 method 是 public 或者 private）就是 module method 且 instance method 也會(huì)變成 private method，對(duì)于被 include 所在的 class 來(lái)說(shuō)是 private method，object.module_name 會(huì)出錯(cuò)。module method 都能被 module_name.method_name 調(diào)用，沒(méi)有被 module_function 標(biāo)記的 public method 不能被 module_name.method_name 調(diào)用。

module 中的 module_function 會(huì)把 module 中的 method 變成 module method 且對(duì)于被 include 所在的 class 來(lái)說(shuō)，module method 在 module 中是 private method 故 module_name.module_method 能調(diào)用，而不能被 object.module_name 調(diào)用。

module 中的 public method 對(duì)于被 include 所在的 class 來(lái)說(shuō)是 instance method,故 object.public_method_in_module 能調(diào)用。如果想要非 module method 能夠被 module 調(diào)用(module_name.not_module_method) ，需要引入 extend self （下文會(huì)討論 extend self）

# test.rb
module MyModule
 def public_meth
  p "a public method, if the module is included to a class , can be call as object.public_meth"
 end
 def module_method
  p "a module method,can be called as module_name.module_method. but can not be call as object.module_method"
 end
 private
 def private_method_to_module_function
  p "a private_method, but can be call as module_name.module_method, because it was assigned to module_function"
 end
 def private_method
  p "I am a private method"
 end
 module_function :module_method, :private_method_to_module_function
end

MyModule.module_method
MyModule.private_method_to_module_function
begin
 MyModule.public_meth
rescue
 p "public method can not be called by module_name.public_meth"
end
begin
 MyModule.private_method
rescue NoMethodError
 p "private method can not be called by module_name.module_method"
end

class MyClass
 include MyModule
end

obj = MyClass.new
obj.public_meth

begin
 obj.private_method
rescue NoMethodError
 p "private method in module can not be call by object.method_name"
end

begin
 obj.module_method
rescue NoMethodError
 p "module method can not be called by object.method_name, for object, module method is private instance method"
end

#調(diào)用
ruby test.rb
"a module method,can be called as module_name.module_method. but can not be call as object.module_method"
"a private_method, but can be call as module_name.module_method, because it was assigned to module_function"
"public method can not be called by module_name.public_meth"
"private method can not be called by module_name.module_method"
"a public method, if the module is included to a class , can be call as object.public_meth"
"private method in module can not be call by object.method_name"
"module method can not be called by object.method_name, for object, module method is private instance method"

總結(jié)就是

•The method will be copied to class' singleton class
•The instance method's visibility will become private

extend self

Include is for adding methods to an instance of a class and extend is for adding class methods

extend 本質(zhì)是給 class 或者 module 添加 class method

extend self 讓 module 中的 instance method 能夠被 module_name.instance_method 調(diào)用，保留 module 中原本 method 的 public 或 private 屬性，但又不像 module_function 一樣把被標(biāo)記的 method 變成 private 。

#!/usr/bin/env ruby
# encoding: utf-8
# test_extend.rb
module MyModule
 extend self
 def public_meth
  p "a public_method extended by self can be called by module_name.public_meth and object.public_meth, included by a class"
  private_method
 end
 private
 def private_method
  p "a private method, can be call in module internal"
 end
end

class MyClass
 include MyModule
end

MyModule.public_meth

begin
 MyModule.private_method
rescue NoMethodError
 p "private method in extend self module can not be called module_name.private_method"
end

obj = MyClass.new
obj.public_meth

begin
 obj.private_method
rescue NoMethodError
 p "private method can not be called by object.private_method"
end

# 調(diào)用 ruby test_extend.rb
"a public_method extended by self can be called by module_name.public_meth and object.public_meth, included by a class"
"a private method, can be call in module internal"
"private method in extend self module can not be called module_name.private_method"
"a public_method extended by self can be called by module_name.public_meth and object.public_meth, included by a class"
"a private method, can be call in module internal"
"private method can not be called by object.private_method"

總結(jié)就是：
•No method copying involved
•No changes to method visibility

總結(jié)

module_function 改變 module 內(nèi) 原來(lái) method 的 public/private 屬性并把改 method 變成 module method ,能夠被 module_name.module_method 調(diào)用。

extend self 就是在 module 自繼承，不改變 module 中 method 的 public/private 屬性，能夠被 module_name.public_method

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