Ruby,mixin实例变量和方法 [英] Ruby, mixin instance variables and methods
问题描述
我有两个文件,一个文件带有模块ToMix
:
I have two files, one with module ToMix
:
module ToMix
@module_var = "modulevar"
def self.mix_function
puts "mix_function SELF: #{@module_var}"
end
def mix_function
puts "mix_function: #{@module_var}"
end
class MixClass
attr_accessor :mixclassvar
def initialize(value)
@mixclassvar = value
end
end
end
我想混入另一个文件中的类TestInclude
的
:
which I want to mixin to the class TestInclude
in the other file:
class TestInclude
require "ToMixFile"
include ToMix
end
有人可以解释为什么未定义实例变量@module_var
和方法self.mix_function
,mix_function
吗?我该如何定义它们?
Could someone explain why the instance variable @module_var
and methods self.mix_function
, mix_function
are undefined? And how would I define them?
t2 = TestInclude.new()
t2.mix_function # => error undefined (exected call to mix_function)
t2.module_var = "test set module_var" # => error undefined
TestInclude.mix_function # => error undefined (expected call to self.mix_function)
TestInclude.method_defined? :mix_function # => false
推荐答案
模块向事物添加函数; attr_accessor
添加了用于与变量进行交互的功能.
Modules add functions to things; attr_accessor
adds functions for interacting with a variable.
module ToMix
@module_var = "module_var"
attr_accessor :mixed_var
def initialize
@mixed_var = "mixed_var"
end
def mix_function
puts "mix_function: #{@mixed_var}"
end
def self.module_function
@module_var
end
end
class Mixed
include ToMix
end
Mixed.new.mixed_var
值得注意的是,
"".extend(ToMix).mixed_var == nil # no error, but no value, interesting!
但是
(a = "".extend(ToMix)).mixed_var = "interesting"
a.mixed_var == "interesting"
和
ToMix.module_function == "module_var"
https://stackoverflow.com/a/151774/171916 http://www.natontesting .com/2009/09/28/access-instance-variables-declared-in-ruby-modules/ 如何在Ruby中动态更改继承
如果我错了,那比我应该纠正的要聪明的多,但是模块和类定义本身就是对象.因此,在模块定义中定义@var
会将var添加到模块对象本身
Those wiser than I should correct me if I'm wrong, but module and class definitions are themselves objects. Defining a @var
in a module definition thus adds the var to the module object itself
比我更正的建议还更明智:类和模块定义的行为类似于单例,但它们本身并不是对象.您可以将方法外部的def self.bacon
和@var
视为c ++静态方法和变量,但是即使您在实例中,它们也可以像静态一样被访问.
Those wiser than I have corrected me: While class and module definitions sort of behave like a singleton, they are not themselves objects. You can think of def self.bacon
and @var
outside of methods as c++ static methods and variables, but they can /only/ be access like a static, even if you're in an instance.
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