Ruby实例变量还是局部变量? [英] Ruby Instance Variables or Local Variables?

问题描述

我是Ruby语言的新手.我明白

I am new to Ruby language. I understand that

@@count: Class variables
@name: Instance variables
my_string: Local variables

我谨记以上几点.但是，我发现了一个这样的Ruby代码:

I keep the above in mind. However, I found one Ruby code like this:

class HBaseController < ApplicationController
...
  def result
    conn = OkHbase::Connection.new(host: 'localhost', port: 9090, auto_connect: true)
  ...
  end
end

'conn'使我很困惑.

'conn' confuses me a lot.

"conn"是实例变量还是局部变量?那么"conn"的范围是什么?

Is 'conn' a instance variable, or local variable? And what is the scope of 'conn'?

推荐答案

我尝试用一​​个小例子来解释它:

I try to explain it with a little example:

class MyClass
  def meth
    conn = 1
  end
  def result
    conn
  end
end

x = MyClass.new
p x.result #-> test.rb:6:in `result': undefined local variable or method `conn'

conn是未知的.让我们尝试先调用meth:

conn is unknown. Let's try to call meth before:

class MyClass
  def meth
    conn = 1
  end
  def result
    conn
  end
end

x = MyClass.new
x.meth      # try to create conn
p x.result  #-> test.rb:6:in `result': undefined local variable or method `conn' 

相同的结果.因此conn是没有实例变量.您在meth中定义了局部变量，但在外部它是未知的.

Same result. So conn is no instance variable. You define a local variable in meth but it is unknown outside.

让我们尝试使用实例变量:

Let's try the same with instance variables:

class MyClass
  def meth
    @conn = 1
  end
  def result
    @conn
  end
end

x = MyClass.new
p x.result  #-> nil (no value assigned (*), but is is existing)
x.meth      # initialze @conn with a value
p x.result  #-> 1

使用访问器方法，您可以隐式定义一个实例变量:

With the usage of accessor-methods you define implicit an instance variable:

class MyClass
  attr_reader :conn
  def meth
    conn = 1
  end
  def result
    conn
  end
end

x = MyClass.new
p x.result  #-> nil (no value assigned (*), but is is existing)
x.meth      #   define conn with a value
p x.result  #-> nil - the instance variable is not changed, a locale variable was used

在方法result中，conn是读取器方法conn.在方法meth中，它是一个区域设置变量(这可能会造成混淆，因为现在您拥有一个与变量同名的变量.

In method result the conn is the reader method conn. In the method meth it is a locale variable (this can be confusing, because now you have a variable with the same name as a variable.

如果要更改meth方法中的conn值，则必须定义一个setter并使用self.conn:

If you want to change the conn-value in the meth-method you must define a setter and use self.conn:

class MyClass
  attr_reader :conn
  attr_writer :conn
  def meth
    self.conn = 1
  end
  def result
    conn
  end
end

x = MyClass.new
p x.result  #-> nil (not defined yet, but is is existing)
x.meth      #   define conn with a value
p x.result  #-> 1

您可以将attr_reader和attr_writer替换为attr_accessor.

(*)备注:我写了未分配值-这不是真的正确，nil也是一个值.

(*) Remark: I wrote no value assigned - this is not really correct, nil is also a value.

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