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无法访问ruby中受保护的方法

ruby-on-rails-4 ruby

AConsumer · 技术社区 · 6 年前

我正在学习红宝石封装的概念。

下面是示例代码,笔记本电脑从机器继承,我已经吃了一个受保护的方法(机器类),但不能通过笔记本电脑的实例访问。

另外,我无法访问笔记本电脑的名为description的受保护方法。

class Machine

  attr_accessor :name,:cost  generated

  protected
  def eat
    puts "machine don't eat"
  end

end


class Laptop < Machine

  private
  def ram
    return "4gb"
  end

  private
  def core
    return "i3"
  end

  protected
  def description
    puts "The laptop has #{ram} ram and it has #{core} core"
  end
end

laptop=Laptop.new
laptop.name="hp_notebook_15_n205tx"
laptop.cost =44000

puts "laptop is a machine, & #{laptop.eat} "  #doesn't work
puts "#{laptop.name} costs #{laptop.cost}"
puts "#{laptop.description}"                  #doesn't work

下面是我得到的错误:

`<top (required)>': protected method `eat' called for #<Laptop:0x2ed3b68 @name="hp_notebook_15_n205tx", @cost=44000> (NoMethodError)
    from -e:1:in `load'
    from -e:1:in `<main>'

0 回复 | 直到 6 年前

ptierno 6 年前

受保护的方法只能由封装在类或子类本身中的方法调用,而不是直接从类/子类的实例调用。如果你想 eat 要从实例调用而不是将其公开或从其他公共方法调用的方法:

[19] pry(main)> class Machine
[19] pry(main)*   protected
[19] pry(main)*   def eat
[19] pry(main)*     puts "eating"
[19] pry(main)*   end
[19] pry(main)* end
:eat
[20] pry(main)> class Laptop < Machine
[20] pry(main)*   def chow
[20] pry(main)*     self.eat
[20] pry(main)*   end
[20] pry(main)* end
:chow
[21] pry(main)> l = Laptop.new
#<Laptop:0x007f9c92b5c968>
[22] pry(main)> l.chow
eating
nil

zeitnot 6 年前

除了动态调度之外,您不能从Ruby外部获得受保护的或私有的方法。我的意思是 laptop.eat 但会引起例外, laptop.send(:eat) 将使运行方法。这是动态调度。

AConsumer 6 年前

方法和常量的可见性或访问权限可以设置为方法公共的、私有的或受保护的。
ruby不允许您访问或更改实例变量表单课外活动。为了克服这个问题,您必须使用访问器方法
只能在类内调用私有方法,而不是从类本身的实例也不与self关键字一起使用

受保护的方法只能由封装在类或子类本身中的方法调用,而不是直接从类/子类的实例调用。

 class Machine
  attr_accessor :name,:cost

  # All the methods below the  protected keyword will be protected
  protected

  def eat
    puts "machine don't eat"
  end

  def sleep
    puts "machine don't sleep"
  end

end

machine=Machine.new
machine.name ="Keyword"
puts "The name of the machine is #{machine.name}"

# NoMethodError  because of accessing the protected methods via an object of Machine
# puts machine.eat
# puts machine.sleep

class Laptop < Machine

  # All the method below the private keyword be will private
  private

  def ram                                 # private method
    return "4gb"
  end

  def core                                # private method
    return "i3"
  end

  # all the methods below the protected keyword will be protected
  public

  def description
    puts "The laptop has #{ram} ram and it has #{core} core"
  end

  def laptopActivity
    eat
    sleep
  end
end

laptop=Laptop.new
laptop.name="hp_notebook_15_n205tx"
laptop.cost =44000

# puts "laptop is a machine, & #{laptop.eat}"   NoMethodError coz trying to access protected method through the object
puts "#{laptop.name} costs #{laptop.cost}"     #accessing public method of Machine through the laptop object
puts "#{laptop.description}"                   # made description public ( description method calls private method of laptop class)
puts laptop.laptopActivity                     # calling protected methods of parent class (inheritance)