ruby 中的实例变量

发布于 2024-10-07 00:39:11 字数 666 浏览 7 评论 0原文

class Test
   def initialize
     @var = "125"
   end
   def testmethod
     puts @var
     puts "accessing me from child class"
   end
 end

class TestExtension < Test

  def method1
    puts @var = "One Hundred and twenty five"
    testmethod()
  end
end

t = Test.new
p = TestExtension.new
p.method1
t.testmethod

输出：

One Hundred and twenty five
One Hundred and twenty five
accessing me from child class
125
accessing me from child class

我的问题是，访问子类 TestExtension 中的 testmethod() 会导致访问在 @var 中声明的值code>TestExtension 类，而不是访问 Test 类中声明的值。正确吗？

原文

class Test
   def initialize
     @var = "125"
   end
   def testmethod
     puts @var
     puts "accessing me from child class"
   end
 end

class TestExtension < Test

  def method1
    puts @var = "One Hundred and twenty five"
    testmethod()
  end
end

t = Test.new
p = TestExtension.new
p.method1
t.testmethod

output:

One Hundred and twenty five
One Hundred and twenty five
accessing me from child class
125
accessing me from child class

My question is that accessing the testmethod() in child class TestExtension results in accessing that value of @var which is being declared in TestExtension class instead of accessing the value which is being declared in Test class . Is it correct ?

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蓝天 2024-10-14 00:39:11

简短回答：
是的

答案稍长：
顾名思义，实例变量是针对每个实例的。对于每个对象，只能有一个名为 @var 的变量，无论哪个类具有访问它的代码。

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时光沙漏 2024-10-14 00:39:11

这是正确的。

正如 Gareth 所说，实例变量属于实例，而不是类。

如果你希望变量属于类，你可以使用类对象的实例变量（呃，这个术语写起来太复杂了）。

简而言之，Ruby 中的一切都是对象，包括类。在下面的示例中，Base 和 Derivative 只是包含对象引用的常量。这些对象代表类（ta-da！）。

考虑到这一事实，我们可以执行以下操作：

class Base
  @var = 1

  def self.change(new_value)
    @var = new_value
  end

  def self.to_s
    "#{self.name}, @var = #{@var}"
  end  
end

class Derivative < Base; end

Derivative.change(2)

puts Base         # => Base, @var = 1
puts Derivative   # => Derivative, @var = 2

It is correct.

As Gareth said, instance variables belong to instances, not classes.

If you want variables to belong to classes, you may use instance variable of class object (err, this term is to complex to write it correctly).

In short, everything in Ruby is an object, including classes. In the following example Base and Derivative are just constants which contain a reference to objects. Those objects represent classes (ta-da!).

Taking this fact into account, we can do the following:

class Base
  @var = 1

  def self.change(new_value)
    @var = new_value
  end

  def self.to_s
    "#{self.name}, @var = #{@var}"
  end  
end

class Derivative < Base; end

Derivative.change(2)

puts Base         # => Base, @var = 1
puts Derivative   # => Derivative, @var = 2

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