Ruby 中的 module_function 和 extend self異同
在閱讀開源的 Ruby 代碼和編寫可維護性的代碼經(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 module 被 include 進一個 class ,那么 module 中的 method (注：沒有被 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 也會變成 private method，對于被 include 所在的 class 來說是 private method，object.module_name 會出錯。module method 都能被 module_name.method_name 調(diào)用，沒有被 module_function 標(biāo)記的 public method 不能被 module_name.method_name 調(diào)用。
module 中的 module_function 會把 module 中的 method 變成 module method 且對于被 include 所在的 class 來說，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 對于被 include 所在的 class 來說是 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 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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