over.rb

irb(main):010:0> class A; def dupa(x); x; end; end
=> nil
irb(main):012:0> module Over; def dupa(x); x + 1; end; end
=> nil
irb(main):013:0> A.new.dupa(1)
=> 1
irb(main):014:0> A.new.extend(Over).dupa(1)
=> 2


irb(main):015:0> class B; def self.dupa(x); x; end; end
=> nil
irb(main):016:0> B.dupa(1)
=> 1
irb(main):017:0> B.extend(Over).dupa(1)
=> 1