Ruby 中的私有方法和受保护方法

发布于 2024-12-18 11:02:22 字数 582 浏览 2 评论 0原文

以下代码有效：

class MyClass
  def method_a
    method_b
  end

  private
  def method_b
    puts "Hello!"
  end
end

m = MyClass.new
m.method_a

将对 method_b 的调用更改为 self.method_b 但是不起作用：

def method_a
  self.method_b
end

我收到 NoMethodError。我的印象是，在实例方法内部时， self 只是解析为类的实例。 为什么 self.method_b 会导致问题？

注意：当 private 更改为 时，self.method_b 可以工作受保护。

注意：如果将上述方法更改为类方法，则从 method_a 调用 self.method_b 不会抛出 NoMethodError 。

原文

The following code works:

class MyClass
  def method_a
    method_b
  end

  private
  def method_b
    puts "Hello!"
  end
end

m = MyClass.new
m.method_a

Changing the call to method_b to self.method_b however does not work:

def method_a
  self.method_b
end

I get a NoMethodError. I'm under the impression that self just resolves to the instance of the class when inside an instance method. Why does self.method_b cause problems?

Note: self.method_b works when private is changed to protected.

Note: if the above methods are changed to class methods then calling self.method_b from method_a doesn't throw the NoMethodError.

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挽清梦 2024-12-25 11:02:22

这就是 Ruby 中私有方法的工作原理。不能使用显式接收器来调用它们（除非它是 setter 方法；见下文）。

请阅读有关 Pickaxe 的访问控制部分了解更多信息。

名称以 = 结尾的私有方法可以使用 self.method_name = ... 来调用，因为这是区分它们与设置局部变数：

class Foo
  def try
    set_foo(1)            # Invokes private method
    self.set_foo(2)       # ERROR: private method `set_foo' called for ...
    self.send(:set_foo,3) # Invokes private method

    bar = 1               # Sets local variable
    self.bar = 2          # Invokes private method
    self.send(:bar=,3)    # Invokes private method
  end

  private
    def set_foo(v)
      @foo = v
    end
    def bar=(v)
      @bar = v
    end
end

Foo.new.bar = 42          # ERROR: private method `bar=' called for ...

This is how private methods work in Ruby. They cannot be called with an explicit receiver (unless it is a setter method; see below).

Read more in the section on Access Control from the Pickaxe.

Private methods whose names end with an = may be invoked using self.method_name = ... as this is necessary to differentiate them from setting a local variable:

class Foo
  def try
    set_foo(1)            # Invokes private method
    self.set_foo(2)       # ERROR: private method `set_foo' called for ...
    self.send(:set_foo,3) # Invokes private method

    bar = 1               # Sets local variable
    self.bar = 2          # Invokes private method
    self.send(:bar=,3)    # Invokes private method
  end

  private
    def set_foo(v)
      @foo = v
    end
    def bar=(v)
      @bar = v
    end
end

Foo.new.bar = 42          # ERROR: private method `bar=' called for ...

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