为什么 Ruby 模块包含排除模块的单例类？
当在 Ruby 中继承类时，单例类也会被继承：
class A
def self.hello
puts "hello"
end
end
class B < A
end
B.hello #=> "hello"
然而对于模块，情况并非如此：
module M
def self.goodbye
puts "goodbye"
end
end
class A
include M
end
A.goodbye #=> NameError
为了绕过这个限制，许多人诉诸于这个丑陋的黑客：
module M
def self.included(c)
c.extend ClassMethods
end
module ClassMethods
def goodbye
puts "goodbye"
end
end
end
好吧，所以我的问题：背后是否有理论/概念上的原因对模块的限制？或者只是实施上的困难？
在查看了 C 源代码（YARV/MRI）后，我发现存在一个实现困难（不是不可克服的，但都是一样的），但这是唯一的原因吗？这个限制还有其他原因吗？
谢谢
When classes are inherited in Ruby the singleton classes are also inherited:
class A
def self.hello
puts "hello"
end
end
class B < A
end
B.hello #=> "hello"
Yet with modules, this is not the case:
module M
def self.goodbye
puts "goodbye"
end
end
class A
include M
end
A.goodbye #=> NameError
To get around this limitation many ppl resort to this ugly hack:
module M
def self.included(c)
c.extend ClassMethods
end
module ClassMethods
def goodbye
puts "goodbye"
end
end
end
Ok, so my question: is there a theoretical/conceptual reason behind this limitation on modules? or was it just an implementation difficulty?
After looking at the C source code (YARV/MRI) I can identify there is an implementation difficulty (not insurmountable, but one all the same), but is this the sole reason? Are there any other reasons for this limitation?
thanks
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除非有人能提出令人信服的论据，否则我认为限制只是在于实施难度。尽管如此，我最近几天一直在解决这个问题，并且（在测试版中）有一个名为
include_complete的新版本的 include，它解决了这些困难，并允许模块继承像类继承一样工作（带来在单例中）在此处查看该项目： http://github.com/banister/include_complete
并注意该项目仍处于测试阶段，但到目前为止似乎仍然按预期工作
Unless anyone can come up with a compelling argument, i feel that the limitation is just down to implementation difficulty. Nonetheless i've been working on the problem the last couple of days and have (in beta) a new version of include called
include_completethat gets around these difficulties and allows modules inheritance to work like class inheritance (bringing in the singleton)Check out the project here: http://github.com/banister/include_complete
And beware the project is still very much in beta, but still seems to work as desired so far
警告：以下只是猜测。
如果您使用类，则需要单例类方法，因为您依赖它们来创建对象（例如
MyClass.new）。如果您使用模块，则不需要它们，因为您不能纯粹从模块创建对象。Warning: the following is just speculation.
If you're using a class, you'll need singleton class methods, because you rely on them to create the object (eg
MyClass.new). If you're using a module, you don't need them, because you can't create objects purely from a module.