module MyModule
  module ClassMethods
    def string(name)
      module_eval <<-RUBY , __FILE__, __LINE__ + 1
        def #{name}
          raise "#{name}" #line number 6
        end
      RUBY
    end
  end

  def self.included(base)
    base.extend(ClassMethods)
  end
end


class MyClass
    include MyModule

    string :foo
end

m = MyClass.new
m.foo

# results in
# $ ruby ./test.rb 
#./test.rb:6:in `foo': foo (RuntimeError)
#	from ./test.rb:25