Ruby：对类定义的显式范围 [英] Ruby: explicit scoping on a class definition

问题描述

免责声明：取自 ruby​​ koans 的代码

这是来自类中的常量范围。这里是几个类的定义：

This is from a discussion of constants scoping within classes. Here is the defintion of a couple few classes:

class Animal
  LEGS = 4
  def legs_in_animal
    LEGS
  end
end

class MyAnimals
  LEGS = 2

  class Bird < Animal
    def legs_in_bird
      LEGS
    end
  end
end

b $ b

在这一点上， MyAnimals :: Bird.new.legs_in_bird 结果为2，我理解为什么 - 在继承层次之前搜索常量的词法空间

At this point doing MyAnimals::Bird.new.legs_in_bird results in 2 and I understand why--search lexical space for the constant before the inheritance heirarchy.

然后这个类被定义：

class MyAnimals::Oyster < Animal
  def legs_in_oyster
    LEGS
  end
end

教程说，现在调用 MyAnimals :: Oyster.new.legs_in_oyster 导致4，我不能弄清楚。对我来说，Oyster是MyAnimals中的一个嵌套类，因此我期望它的行为方式与Birds类相同。我缺少一些关于什么声明类Oyster与显式范围的手段。一些关键信息。

The tutorial says that now calling MyAnimals::Oyster.new.legs_in_oyster results in 4 and I can't figure it out. It appears to me that Oyster is a nested class in MyAnimals and as such I expected it to behave the same ways as the Birds class did above. I'm missing some key information about what declaring the class Oyster with explicit scoping means.

任何人都可以解释这个给我吗？我已经通过Google找到了数百个ruby类教程，但没有一个解决这种情况。

can anyone explain this to me? I've found hundreds of ruby class tutorials via Google but none of them address this situation.

提前谢谢...

推荐答案

我认为此示例最好地解释。 Ruby按此顺序搜索常量定义：

I think this example explains it best. Ruby searches for the constant definition in this order:

1. 包围范围


2. 顶层


3. 包含的模块


4. 超类


5. 顶级


6. 对象


7. li>
   

1. The enclosing scope
2. Any outer scopes (repeat until top level is reached) Any outer scopes (up to but not including the top level
3. Included modules
4. Superclass(es)
5. Top level
6. Object
7. Kernel

EDIT

感谢 Mark Amery 来指出这个错误。只有在没有封闭范围和/或超类的情况下才能达到顶层。

Thanks to Mark Amery for pointing out this error. The top-level is only reached in the case where there are no enclosing scopes and/or superclasses. The linked example actually makes this clear, sadly I read it wrong.

这种情况的一个例子：

FOO = 'I pity the foo!'

module One
  FOO = 'one'

  class Two
    FOO = 'two'

    def self.foo
      FOO
    end
  end

  class Three < Two
    def self.foo
      FOO
    end
  end
end

class Four
  class Five < Four
    def self.foo
      FOO
    end
  end
end

describe FOO do
  it "depends where it is defined" do
    expect(FOO).to eq 'I pity the foo!' # top-level
    expect(One::FOO).to eq 'one' # module
    expect(One::Two.foo).to eq 'two' # class
    expect(One::Three.foo).to eq 'one' # outer scope (One) comes before superclass
    expect(Four::Five.foo).to eq 'I pity the foo!' # top-level
  end
end

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