From: Daniel DeLorme <dan-ml@...42.com>
Date: 2008-07-30T00:50:06+09:00
Subject: Re: about class in module

Kyung won Cheon wrote:
> -- test1.rb --
> 
> class C
>   def a
>   end
> end
> 
> class C
>   def a
>     puts "override"
>   end
> end
> 
> puts C.new.a # => override
> 
> -- test2.rb --
> 
> class C
>   def a
>   end
> end
> 
> module M
>   class C
>     def a
>       puts "why not override?"
>     end
>   end
> end
> 
> include M
> 
> puts C.new.a # => nil
> 
> ########################
> # Help Me^^
> ########################

Hhmm, this is actually a little tricky. If I had to hazard a guess I 
would say it's related to the fact that modules included in X are higher 
in the lookup chain than X itself. e.g.:

module M
   def foo; "M-foo" end
   def foo2; "M-foo2" end
end
class A
   def foo; "A-foo" end
   include M
end
A.new.foo #=> "A-foo"
A.new.foo2 #=> "M-foo2"

so I imagine the same rule applies to constant lookups:

module N
   BAR = "N-bar"
   BAR2 = "N-bar2"
end
class B
   BAR = "B-bar"
   include N
end
B::BAR #=> "B-bar"
B::BAR2 #=> "N-bar2"

With warnings enabled, you would have seen that your test1.rb outputs:
   (irb):8: warning: method redefined; discarding old a

--
Daniel