Why not we able to include module in the parent class from child class?

ruby-talk
1

I am having some confusion with the `include` method in Ruby, to include
a module in a parent class, which is defined in a child class of that
parent class.

class B
  module M
    def meth
      11
    end
  end
end

class A < B
end
A.new.meth # undefined method `meth' for #<A:0x9780bdc> (NoMethodError)

I am fine with above.

class B
  module M
    def meth
      11
    end
  end
end

class A < B
   include M
end
A.new.meth # => 11

still I am fine with this.

Why I am not able to do the below?

class A
   include B::M
end

class B < A
  module M
    def meth
      11
    end
  end
end
# ~> -:2:in `<class:A>': uninitialized constant A::B (NameError)
# ~> from -:1:in `<main>'

···

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2

Typing order. When ruby sees you including B::M neither B nor B::M have
been defined yet.

···

Sent from my phone, so excuse the typos.
On Nov 27, 2013 6:52 AM, "Love U Ruby" <lists@ruby-forum.com> wrote:

I am having some confusion with the `include` method in Ruby, to include
a module in a parent class, which is defined in a child class of that
parent class.

class B
  module M
    def meth
      11
    end
  end
end

class A < B
end
A.new.meth # undefined method `meth' for #<A:0x9780bdc> (NoMethodError)

I am fine with above.

class B
  module M
    def meth
      11
    end
  end
end

class A < B
   include M
end
A.new.meth # => 11

still I am fine with this.

Why I am not able to do the below?

class A
   include B::M
end

class B < A
  module M
    def meth
      11
    end
  end
end
# ~> -:2:in `<class:A>': uninitialized constant A::B (NameError)
# ~> from -:1:in `<main>'

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