在 Ruby 中，有没有办法“覆盖"子类中的常量，以便继承的方法使用新常量而不是旧常量? [英] In Ruby, is there a way to 'override' a constant in a subclass so that inherited methods use the new constant instead of the old?

问题描述

在 Ruby 中，是否有一种方法可以覆盖"子类中的常量，这样从子类调用继承的方法会导致该方法使用新常量而不是旧常量?例如:

In Ruby, is there a way to 'override' a constant in a subclass in such a way that calling an inherited method from the subclass results in that method using the new constant instead of the old one? For example:

class SuperClass
  CONST = "Hello, world!"
  def self.say_hello
    CONST
  end
end

class SubClass < SuperClass
  override_const :CONST, "Hello, Bob!"
end

SuperClass.say_hello # => "Hello, world!"
SubClass.say_hello   # => "Hello, Bob!"

如果没有，有没有办法做这样的事情呢?

If not, is there perhaps a way to do something like this instead?

class SuperClass
  CONST = "Hello, world!"
  def self.say_hello
    CONST
  end
end

SubClass = SuperClass.clone
SubClass.send(:remove_const, :CONST)
SubClass.const_set(:CONST, "Hello, Bob!")

SubClass.say_hello # => "Hello, Bob!"

<小时>

注意:我在 irb 中尝试了我的第二个示例，它似乎可以工作，只是在克隆类后类方法似乎无法访问 CONST:

---

Note: I tried my second example out in irb, and it seems to work except that class methods can't seem to access CONST after I clone the class:

irb(main):012:0> SubClass.say_hello
NameError: uninitialized constant Class::CONST
        from (irb):4:in `say_hello'
        from (irb):12
        from C:/Ruby193/bin/irb:12:in `<main>'

推荐答案

我通过简单地重新定义子类中的常量，然后在方法中将其引用为 self.class::CONST 在实例方法中， self::CONST 在类方法中.在您的示例中:

I've done this by simply redefining the constant in the subclass, and then referring to it in methods as self.class::CONST in instance methods and self::CONST in class methods. In your example:

class SuperClass
  CONST = "Hello, world!"
  def self.say_hello
    self::CONST
  end
end

class SubClass < SuperClass
  CONST = "Hello, Bob!"
end

SubClass.say_hello #=> "Hello, Bob!"

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