Donald Luo wrote:

> module A
>   extend self
>   def a
>     p 'a'
>   end
> end
> 
> class C
>   include A
> end
> 
>> C.a
> NoMethodError: undefined method `a' for C:Class
> 
> Anyone can explain this?

Module functions are not transfered by include by default. You could do 
this:

class C
   include A
   extend A
end

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