ruby - Ruby 作用域、常量优先级：词法作用域或继承树

Question

我将向您展示ruby​​koans教程中的代码片段。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（尽管它打算用粗体显示））。有人可以解释一下吗？提前致谢！

Answer 1

这在这里得到了回答：Ruby: explicit scoping on a class definition。但也许不是很清楚。如果您阅读链接的文章，它将帮助您找到答案。

基本上，Bird在 的范围内声明，MyAnimals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。

插入p Module.nesting每个类，向您展示封闭范围是什么。

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]

看到不同？