如何在继承类中使用重写常数

given this code:

鉴于这种代码:

class A
  CONST = 'A'

  def initialize
    puts CONST
  end
end

class B < A
  CONST = 'B'
end

A.new # => 'A'
B.new # => 'A'

I'd like B to use the CONST = 'B' definition, but I don't know how. Any ideas?

我希望B使用CONST = 'B'的定义，但我不知道怎么用。什么好主意吗?

Greetings

问候

Tom

汤姆

4 个解决方案

#1

class A
  CONST = 'A'

  def initialize
    puts self.class::CONST
  end
end

class B < A
  CONST = 'B'
end

A.new # => 'A'
B.new # => 'B'

#2

Sorry I couldn't get the code formatting to work in a 'comment' only in an 'answer' but this is in response to akostadinov's question to Hendrik "how is this different from his [Konstantin's] answer?"

抱歉，我不能让代码格式只在'注释'中工作，而这是针对akostadinov问Hendrik的问题“这和他[Konstantin]的答案有什么不同?”

I'd guess Hendrik was trying to access the constant from methods in his inheriting class & that depends on if it's an instance or static method. It seems to behave as you'd expect in an instance method. But maybe or maybe not how you'd expect for a static method. Even if that's not what Hendrik meant, this may be worth noting:

我猜亨德里克试图从继承类的方法中访问常量&这取决于它是实例还是静态方法。它的行为似乎与您在实例方法中预期的一样。但是，也许你对静态方法的期望不是这样的。即使亨德里克不是这个意思，这也值得注意:

If you have the exact class definitions as Konstantin, but you add a method to class A like this:

如果您有确切的类定义如Konstantin，但您添加一个方法到类a，如:

def self.print_const
  puts CONST
end

Then you get A both times:

然后你得到两个A:

A.print_const # prints A
B.print_const # prints A

However if you define the method in A by referencing the class:

但是，如果您通过引用类来定义方法A:

def self.print_const
  puts self::CONST
end

Then you get:

然后你会得到:

A.print_const # prints A
B.print_const # prints B

#3

I had a few issues with the solution by Konstantin Haase. When accessing the constant in an instantiated object of the inheriting class, the parent constant was used.

我对Konstantin Haase的解决方案有一些疑问。当访问继承类的实例化对象中的常量时，使用父常量。

I had to explicitly refer to the class.

我必须明确地提到这个类。

self.class::CONST

cheers

干杯

#4

In case anyone finds this and is using module extension instead, just use

如果有人发现了这个，并且正在使用模块扩展，那么就使用。

self::CONST

自我:常量

#1

class A
  CONST = 'A'

  def initialize
    puts self.class::CONST
  end
end

class B < A
  CONST = 'B'
end

A.new # => 'A'
B.new # => 'B'

#2