Ruby 范围，常量优先级 : lexical scope or inheritance tree

Question

我将向您展示来自 rubykoans 的代码片段教程。考虑下一个代码:

class MyAnimals
LEGS = 2

  class Bird < Animal
    def legs_in_bird
      LEGS
    end
  end
end

def test_who_wins_with_both_nested_and_inherited_constants
  assert_equal 2, MyAnimals::Bird.new.legs_in_bird
end

# QUESTION: Which has precedence: The constant in the lexical scope,
# or the constant from the inheritance hierarchy?
# ------------------------------------------------------------------

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

def test_who_wins_with_explicit_scoping_on_class_definition
  assert_equal 4, MyAnimals::Oyster.new.legs_in_oyster
end

# QUESTION: Now which has precedence: The constant in the lexical
# scope, or the constant from the inheritance hierarchy?  Why is it
# **different than the previous answer**?

实际上问题在评论中(我用星号突出显示了它(尽管它打算以粗体显示))。有人可以解释一下吗？提前致谢!

Answer 1

这里有答案:Ruby: explicit scoping on a class definition .但也许它不是很清楚。如果您阅读链接的文章，它将帮助您找到答案。

基本上，Bird 是在 MyAnimals 的范围内声明的，在解析常量时具有更高的优先级。 Oyster 位于 MyAnimals 命名空间中，但未在该范围内声明。

将 p Module.nesting 插入到每个类中，并显示封闭范围是什么。

class MyAnimals
  LEGS = 2

  class Bird < Animal

    p Module.nesting
    def legs_in_bird
      LEGS
    end
  end
end

产量:[AboutConstants::MyAnimals::Bird, AboutConstants::MyAnimals, AboutConstants]

和

class MyAnimals::Oyster < Animal
  p Module.nesting

  def legs_in_oyster
    LEGS
  end
end

产量:[AboutConstants::MyAnimals::Oyster, AboutConstants]

看出区别了吗？