从类外部访问实例变量 [英] Access instance variable from outside the class

问题描述

如果实例变量属于一个类，是否可以使用类实例直接访问该实例变量(例如@hello)?

If an instance variable belongs to a class, can I access the instance variable (e.g. @hello) directly using the class instance?

class Hello
  def method1
    @hello = "pavan"
  end
end

h = Hello.new
puts h.method1

推荐答案

是的，您可以像这样使用instance_variable_get:

Yes, you can use instance_variable_get like this:

class Hello
  def method1
    @hello = "pavan"
  end
end

h = Hello.new
p h.instance_variable_get(:@hello) #nil
p h.method1                        #"pavan" - initialization of @hello
p h.instance_variable_get(:@hello) #"pavan"

如果变量未定义(在我的示例中为第一次调用instance_variable_get)，则会得到nil.

If the variable is undefined (first call of instance_variable_get in my example) you get nil.

如安德鲁(Andrew)在其评论中所述:

As Andrew mention in his comment:

您不应将此方法作为访问实例变量的默认方式，因为它违反了封装.

You should not make this the default way you access instance variables as it violates encapsulation.

更好的方法是定义访问器:

A better way is to define an accessor:

class Hello
  def method1
    @hello = "pavan"
  end
  attr_reader :hello  
end

h = Hello.new
p h.hello #nil
p h.method1                        #"pavan" - initialization of @hello
p h.hello #"pavan"

如果要使用其他方法名称，则可以别名访问器:alias :my_hello :hello.

If you want another method name, you could alias the accessor: alias :my_hello :hello.

如果该类不是在代码中定义的，而是在gem中定义的:您可以向类中插入新功能.

And if the class is not defined in your code, but in a gem: You can modify classes in your code and insert new functions to classes.

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