@instance_variable 和 attr_accessor 的区别 [英] Difference between @instance_variable and attr_accessor

问题描述

我刚开始学习 ruby​​，我没有看到 @instace_variable 和使用 attr_accessor 声明的属性之间的区别.

I Just started learning ruby and I don't see the difference between an @instace_variable and an attribute declared using attr_accessor.

以下两个类有什么区别:

What is the difference between the following two classes:

class MyClass  
  @variable1 
end

和

class MyClass
  attr_accessor :variable1
end

我在网上搜索了很多教程，每个人都使用不同的符号，它与ruby版本有什么关系吗?我还在 StackOverflow 中搜索了几个旧线程

I searched lot of tutorials online and everybody uses different notation, Does it have to do anything with the ruby version? I also searched few old threads in StackOverflow

Ruby 中的 attr_accessor 是什么?
这两个 Ruby 类初始化定义有什么区别?

但我仍然不知道什么是最好的使用方式.

But still I am not able to figure out what is the best way to use.

推荐答案

实例变量在它所在的对象之外不可见；但是当您创建一个 attr_accessor 时，它会创建一个实例变量，并使其在对象外可见(和可编辑).

An instance variable is not visible outside the object it is in; but when you create an attr_accessor, it creates an instance variable and also makes it visible (and editable) outside the object.

实例变量示例(不是attr_accessor)

class MyClass
  def initialize
    @greeting = "hello"
  end
end

m = MyClass.new
m.greeting #results in the following error:
  #NoMethodError: undefined method `greeting' for #<MyClass:0x007f9e5109c058 @greeting="hello">

使用attr_accessor的示例:

class MyClass
  attr_accessor :greeting

  def initialize
    @greeting = "hello"
  end
end

m2 = MyClass.new
m2.greeting = "bonjour" # <-- set the @greeting variable from outside the object
m2.greeting #=> "bonjour"   <-- didn't blow up as attr_accessor makes the variable accessible from outside the object

希望能说明一切.

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