Ruby-on-rails Rails 模块中的 mattr_accessor 是什么？
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What is mattr_accessor in a Rails module?
提问by JasonOng
I couldn't really find this in Rails documentation but it seems like 'mattr_accessor'is the Modulecorollary for 'attr_accessor'(getter & setter) in a normal Ruby class.
我在 Rails 文档中真的找不到这个，但似乎“mattr_accessor”是普通 Ruby类中“attr_accessor”（getter & setter）的模块推论。
Eg. in a class
例如。在一个班级
class User
attr_accessor :name
def set_fullname
@name = "#{self.first_name} #{self.last_name}"
end
end
Eg. in a module
例如。在一个模块中
module Authentication
mattr_accessor :current_user
def login
@current_user = session[:user_id] || nil
end
end
This helper method is provided by ActiveSupport.
此辅助方法由ActiveSupport提供。
回答by Avdi
Rails extends Ruby with both mattr_accessor(Module accessor) and cattr_accessor(as well as _reader/_writerversions). As Ruby's attr_accessorgenerates getter/setter methods for instances, cattr/mattr_accessorprovide getter/setter methods at the classor modulelevel. Thus:
Rails 使用mattr_accessor（模块访问器）和cattr_accessor（以及 _ reader/_writer版本）扩展了 Ruby 。作为Ruby的attr_accessor生成用于getter / setter方法的实例，cattr/mattr_accessor提供在吸气/ setter方法类或模块的水平。因此：
module Config
mattr_accessor :hostname
mattr_accessor :admin_email
end
is short for:
简称：
module Config
def self.hostname
@hostname
end
def self.hostname=(hostname)
@hostname = hostname
end
def self.admin_email
@admin_email
end
def self.admin_email=(admin_email)
@admin_email = admin_email
end
end
Both versions allow you to access the module-level variables like so:
两个版本都允许您访问模块级变量，如下所示：
>> Config.hostname = "example.com"
>> Config.admin_email = "[email protected]"
>> Config.hostname # => "example.com"
>> Config.admin_email # => "[email protected]"
回答by Orion Edwards
Here's the source for cattr_accessor
And
和
Here's the source for mattr_accessor
As you can see, they're pretty much identical.
如您所见，它们几乎相同。
As to why there are two different versions? Sometimes you want to write cattr_accessorin a module, so you can use it for configuration info like Avdi mentions.
However, cattr_accessordoesn't work in a module, so they more or less copied the code over to work for modules also.
至于为什么会有两个不同的版本？有时你想cattr_accessor在一个模块中编写，所以你可以将它用于配置信息，如 Avdi 提到的。
但是，cattr_accessor在模块中不起作用，因此他们或多或少地复制了代码以也适用于模块。
Additionally, sometimes you might want to write a class method in a module, such that whenever any class includes the module, it gets that class method as well as all the instance methods. mattr_accessoralso lets you do this.
此外，有时您可能希望在模块中编写类方法，这样无论何时任何类包含该模块，它都会获取该类方法以及所有实例方法。mattr_accessor也可以让你这样做。
However, in the second scenario, it's behaviour is pretty strange. Observe the following code, particularly note the @@mattr_in_modulebits
然而，在第二种情况下，它的行为很奇怪。观察以下代码，特别注意@@mattr_in_module位
module MyModule
mattr_accessor :mattr_in_module
end
class MyClass
include MyModule
def self.get_mattr; @@mattr_in_module; end # directly access the class variable
end
MyModule.mattr_in_module = 'foo' # set it on the module
=> "foo"
MyClass.get_mattr # get it out of the class
=> "foo"
class SecondClass
include MyModule
def self.get_mattr; @@mattr_in_module; end # again directly access the class variable in a different class
end
SecondClass.get_mattr # get it out of the OTHER class
=> "foo"
