instance_eval_weirdness.rb

irb --> RUBY_VERSION
    ==> "1.9.1"

irb --> module M
  module A
    def execute(&block)
      instance_eval(&block)
    end
  end
end

module N
  class B
  end

  class C
    include M::A

    def with_instance_eval
      execute { B.new }
    end

    def without_instance_eval
      B.new
    end

  end
end
    ==> nil

irb --> c = N::C.new
    ==> #<N::C:0x00000101030750>

irb --> c.without_instance_eval
    ==> #<N::B:0x0000010101ff48>

irb --> c.with_instance_eval
NameError: uninitialized constant N::C::B

irb --> c.instance_eval { B.new }
NameError: uninitialized constant N::C::B

irb --> c.instance_eval { N::B.new }
=> #<N::B:0x000001009b1930>